I also have had great success with a peel and stick weatherstrip on an action packer. I had one bolted onto my roof rack for 9 months in Australia. It was subject to massive amounts of "Bulldust", several huge rain downpours at highway speeds, and temperatures into the mid 40's Celsius (113 F...
I highly recommend truck bed liner. I made a plywood shelf for my rear bumper that I had professionally coated in truck bed liner. It was a step and a shelf to support a propane tank and folding ladder. It withstood all kinds of abuse, sun and water with no signs of deterioration or fading.
I like it! The concept is very similar to the XP V2 & V3 but using flat panels. I don't see any technical issues with building the lower half of the clamshell design from off the shelf foam/composite panels. The top sides of the lower clamshell will tend to flex a lot, but can easily be braced...
More NWOR photos:
This gets my vote for best outdoor kitchen at the rally (Echo trailer):
I like the Nemo awnings on the AT Habitat:
A very cool custom camper using a Flip Pac roof:
This is the longest vehicle I saw at the rally, check out the rear overhang!