Whatever would work best, I believe most jet sleds and otter sleds are made from polyethylene. It will be used for goose and duck hunting, to haul decoys but for me to lay in when I'm in the field. Live on a farm so if I'm not sure what I'm doing someone in the family should.
I just did a search based on the picture you posted, on google, for the cost of one, they were all less than $60 bucks, I would just buy one, you are looking at a lot of work to make one?
One other thing, if you have a local good will, salvation army, second hand store, look for an old car top carrier, the old wider clamshell type, then pop the hinge and you have two sleds that can be hooked together and carry even more decoys.