: Skin on frame trailer could work quite well. Dacron works on 200 mph
: aircraft, will probably work fine on a 60 mph trailer
: Should be quite light too.

If that trailer isn't real heavy it will be a big sail-or wing. It could be a nightmare to keep on the road on a windy day. For 17' to 18' kayaks you'd have nearly a 20 foot trailer. That could easily track a foot or two into the next lane if hit with a sidewind. Drivers next to you might not appreciate that. Might be something you would only use on calmer days. Or, make the soft sides removable and reduce the sail effect on the windy days.

Semi trailers with soft sides covering flatbed trailers (also called "curtain-side" trailers use the same truck tarp fabric as other tarps (and this is what Yost uses, too) but simply pull it over a boxy frame. Straps on the sides make loading the trailer easy, and covering the load is as simple as tightening those straps. The material is very durable and water proof. Obviously the various Transportation departments allow this material for vehicle use, so there should be no problem using it on a homebuilt trailer. You can gt the stuff in colors and it can be painted on, so billboard potential is pretty good.

Hope this helps

PGJ