thats what i was planning on doing and but home depot and lowes had only small peices and i wanted one big one so i dont have to worry about leaks. anyways, heres what i did today. i wrapped the frame in some thick plastic sheet that i got from next down the street where they were building a house.
to make it look nice, i ordered vinyl that i'm gonna wrap around a very thin peice of posterboard or plywood or something. this way it will be completly flat and look good.
this part cost me less than $20 and with the vinyl, the whole tonneau will cost me around $50