I have thought about the PVC idea my self. Sometime this summer I need to build a bigger deck for my trailer and have some 16" heavy water main (nearly 1/2" thick) that I've been planning on ripping into strips (maybe 2" wide, what ever looks right when I get to cutting) then lying those convex side up on my deck to act as both a smooth surface and a way of aligning the boat on the trailer. It will also give me a place to stand that is not so slippery (in between runners). For your situation that sounds pretty easy and worth a try. If you do go pvc look at the gray material (UV exposure rated) the white stuff might only last a year or two before becoming brittle.
UHMW would also be a great option, but more expensive. It's easily workable, wood working tools, router, saws etc. Way easier than aluminum.
A buddy on a recent trip had two 2'wide by 10' long strips of UHMW on his trailer. We launched his fully loaded boat with a slight push. We loaded the same mostly loaded boat back onto the trailer with two people pulling with moderate effort. In contrast, my boat on 2X6 runners had to be floated on and off. There was no pushing it off, even with a tilt bed trailer, we had to keep backing until it was almost floating. I've launched my boats as day rigs thousands of time with little effort but had never even tried to launch it fully loaded for a 4 day trip...
The only drawback to UHMW is it shrinks and expands a lot with heat. He's had his trailer rigged with it for years and has gone through several mounting permutations. He last settled on slots with washers and pan head screws. and that has held up several years. The boat rubber rarely contacts the metal fasteners. Prior to this most solutions resulted in snapped off fasteners as the material shrunk or expanded. If I recall the material was pretty expensive; several hundred bucks... for his 4x10' sheet.
Yesterday's gone on down the river and you can't get it back. - Agustus McCrae