Ok here we go
I tried something on my front deck and it seems to be working ok
glassed the back side of my deck put 4 inch strip of clothe down the center line.
then I turned it over ran a saturation coat on the side(the top side)
then drew a line down the center making sure I was in the center of the tape on the other side
I set my skill saw to cut 3/4 way threw the 1/8 ply ( I free handed it should of used a straight edge) but it worked ok
then I got a 2=4 placed it under it and pushed down
Wala a good straight edge in the 1/8 ply no waves
put on top of yak marked then sanded it to shape
Saves a lot of time good straight line and the cloth on the back side works as a hinge to hold everything just right and when you bend it open lets you glass all the way back through to the tape.
Ron