: Yeah i have 3 sit on tops.
: one of them would do great to copy.

: i was thinking cover the sit on top with plastic lawn garbage bag.
: put layers of glass on that...cover with plastic again and dump lots of sand
: on top of that.
: i don't think that will come out good as far as smooth even thickness.

: what do you recommend?

Ross's method will work fine, though removing the seat from a sit on top isn't possible. I'd mask out the seat opening then cover the area around the seat and the rest of the boat (resin gets everywhere) with a heavy plastic drop cloth. If there are drain holes on the seat surface, SOT's seem to have drain holes everywhere, they'll have to be taped over with duct tape.
To insure that nothing sticks to the poly, though not much sticks to poly, I'd both wax with mold release wax and then use PVA, it's a belt and suspenders approach, but better than having glass stuck to your boat. Btw, it's usually recommended to use from 8 to 15 coats of mold release wax in other words lots of wax. Then I'd follow Ross's method of laying up the seat, not all that tricky.

Bill H.