I have used fly line backing 7-10lb. test, it is easy to tie and comes in various colors.
A super light plywood called poplar ply ( used for rc park flyers) makes good decks, not sure if it would work for hull as it likes to break when bent.
tomo,
I don’t use pulleys for my turning blocks, I use #6 or #7 ceramic fishing rod guides. I can see your issue with the smaller stuff getting off the pulley and getting fouled.