Trex is a bit over 2X as heavy as 3/4 marine plywood when both are dry. Trex doesn't absorb water but plywood tends to get much heavier if continuously exposed to moisture. Add carpet and I don't think there would be a huge difference after a few seasons. That aside, for dock usage, the removal of the motor and the old furniture would more than make up the difference. I bought an old 14 ft flatboat that had a plywood, foam, and aluminum subfloor in it. The continuous moisture caused the aluminum to corrode and leak in multiple spots. When I took it to the salvage yard to scrap it, a boat that should have weighed under 200 pounds crossed the scale at 541 pounds. That made up the price difference between dirty and clean aluminum prices.
I plan to do a pictorial of the conversion process if there is any interest.
