Art,
My personal opinion is that plywood (exterior or marine grade) would be  best 
for this application. Strength to weight ratio is higher and easier to work  
with for most people. The UHMWPE is great for making blocks and things, but  
doesn't have the strength that plywood has. Besides, if you are going to  make 
your own, you need something that staples will stick into and stay put.  They 
pull out of plastic easily.
Getting the filler cushions to the same height and having the pad or foam  
the same strength or softness of the cockpit cushions are all important for a  
good fit and feel.
If marine grade ply wood isn't available or you find it cost prohibitive to  
use or order, just ask for an exterior grade. It's the same stuff used for 
roof  sheathing and is somewhat more resistant to moisture than standard grade.
 
Rummy.....gonna burn up the dance floor and go shaggin tonight. The  shag is 
the SC state dance. It's a beach thingy. I'm going to be shagadelic  baby.



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