Ross H

Use the Appearance panel and make a two stroke curve. One is thin and solid the other is thick and dashed, try a pair of settings of 0.1 and 2 for the dashed line. The 2 is the gap, note the squared off no-cap.

 
 

The best option is to draw a segment of about 180x360ps size of that line as b/w. Export as png. Import as new image brush.
Then use this brush with pen tool to draw curves (in Designer).
This allows to hand-paint the lines and give it a retro style.

Refreshing.
It seems that with very few exceptions, user requests for adding features to this exciting new Affinity platform are couched in "me, too" terms. ("I need this single deal-breaking feature now, just as it is in [my pet program], or I'm outta here!").
There's not really much new under the 2D graphics software sun, and hasn't been in a long time. I blame that on the continued dominance of the market by a few historic monoliths.
The good news is, almost every "me, too" feature request is a potential opportunity for breaking beyond the lockstep lethargy of current offerings. My constant hope is that the Affinity team is striving for something more innovative than the conventional wisdom standard-fare.
One of the macro consequences of the decades of micro improvements to the mainstream titles is that in today's increasingly data-driven world, publishing and illustration programs seem farther and farther behind the times.  Just another "me, too" data merge feature like those typically used for recipient address labels, etc. is already passé.
Juha7one mentioned FileMaker and made my heart sing because I've used FileMaker to build fairly ambitious fully data-driven publishing solutions. Two examples:
A 1000-page aftermarket parts catalog, the content of which is directly and continuously updated by parts information experts, not graphic designers, using straightforward data-entry screens, designed to precisely fit and streamline their tasks. The dataset is much larger than what will fit in a thousand-page print, and includes relational tables for brand-to-brand cross-referencing, live pricing, and more. The design is built in, up-front, and is flexible. The layout assembly and export to print-ready PDFs is entirely automated, requiring no "desktop publishing" whatsoever. Workers can on-the-fly isolate focused content by section or part type, and automatically generate print-ready "extracts" from the catalog for monthly specials, trade-show handouts, etc. An application that empowers Dealers to automatically generate their own individualized dealership-branded sales promotions (electronic or in print, in various formats) while keeping in  full agreement with the factory branding standards. The application is a tidy six-step interface start-to-finish. Its dataset includes everything from the above-described product catalog database (access to tens of thousands of items), lookup functionality for current Dealer pricing (including a handy calculator for pricing on a per-item basis), the Dealer's Direct Mail info and indicia, and customer mail list. Those and other projects like them have convinced me of this: It would be far easier to turn a version of FileMaker Pro into a graphically-powerful data-driven publishing platform than to turn a conventional page-layout program into a powerful data-handling solution. All that would be required is to flesh out FileMaker's Layout Mode with a few more graphics-oriented features.
I'm just an enthusiastic FileMaker user, and just mention it from that standpoint. When asked what my favorite "graphics program" of all time is, I only half-jokingly reply, "FileMaker Pro." Its approachability is well within the capabilities of most graphic designers, and for creative minds its use opens a whole world of data-driven publishing capabilities, either standalone or in conjunction with conventional graphics programs.
JET

Another vote for Data Merge. While InDesign's implementation might not be the best, it is a very useful feature. I've used ID's data merge on various projects. Being able to link to images is great and automatically updating a document with a new merge file is a real time saver.

Another vote for Data Merge. While InDesign's implementation might not be the best, it is a very useful feature. I've used ID's data merge on various projects. Being able to link to images is great and automatically updating a document with a new merge file is a real time saver.

Not yet but it's something we want to look at doing for future updates

@Gabe Logan
Welcome to the Serif Affinity forums
It's not possible yet. There are plans to be able to open IDML files in the future
<mod edit> IDML not INDD file clarification was made in an edit on 6th July 2019 </mod edit>

I also think that calling Publisher a "massive fail" at this point is being both unfair and unrealistic. I don't know where Serif is pitching the Affinity suite, and whether they intend to rival Adobe products eventually. But even if that is the goal, Rome wasn't built in a day.
I think when we look at the Affinity suite overall, and Publisher in particular, we should remember that:
Adobe Illustrator first shipped in 1988. Therefore at the time of writing it has had three decades of development effort with a big engineering team and a big budget. Photoshop first shipped in 1990, so again almost three decades of development, and probably an even bigger budget. And they have Thomas Knoll! InDesign shipped in 2000, so we have 18 years of development on this product. All these products have a huge user community, and they have been providing feedback for decades.
So are the Adobe products more refined and more capable? Of course they are, and it has taken Adobe 20 or 30 years to get there. I have worked in software development (also for decades) and I understand how long these things take. Hats off to Serif for even starting this project. Its always easier not to.
What we are talking about with Affinity Publisher is a beta of a V1 product. So yes, it is going to have bugs and shortcomings compared to a product that has been shipping for 18 years. Even if the development team want to eventually build something to rival InDesign or Quark Xpress, that isn't going to happen with V1, or V2, or probably not V3. If they tried to do that it would never ship anything, and Serif wouldn't sell anything and they would be out of business. This is a work in progress, as is all software. Nothing is ever finished.
The same applies with Affinity Photo and Designer. They are "finished" products (i.e. they are shipping as V1.*). But to expect them to be a feature for feature matchup for their Adobe counterparts at this stage just isn't going to happen. I for one would love to see an "Image Trace" feature in Affinity Designer to match AI, and also better "Content Aware" technologies in Affinity Photo to match PS. One day perhaps, but give them time. With any software product from any manufacturer, V1 is always about "time to market". You have to establish a revenue stream to fund further development. They are trying to build a suite of products. I'm sure they know we need a file browser to stand up to Adobe Bridge, and a RAW processor to match Lightroom. But one step at a time.
It has taken InDesign 18 years to get where it is today, and Publisher will also mature over time I'm sure. For what its worth from my first look at Publisher I am encouraged. But its a beta, and that's why we are all here, to contribute to the development effort. Yes I have posted some items and made comparisons with InDesign. but that's because I'm used to that product. I don't expect a feature for feature matchup on day one.
Thanks,
Mike.
 

Data Merge, as InDesign does it at least, is utter rubbish. If you want to implement some sort of batch data import & formatting then look into InDesign's XML importer and Structure panel instead. It's more complicated but infinitely better. And Affinity can "easily" one-up Adobe on this by simply supporting XML and also JSON import. JSON is being used a lot more than XML these days (for the best and for the worse), so supporting it is a big competitive advantage.