the surface of every yak here is finished using the same one off type process. like a cedar or hood armature covered w/ glass and finished(you just want to remove the armature). if you want a smooth surface immediately - vac bag or tightened sheets of wrap may work, but there will be seams and wrinkles that you/d have to finish like all of us w/ scrapers and fairing bds etc. Is this ok?

but the stiffness is the key.

If you have experience that the layup you'll use is stiff enough for your purpose, its straight forward - just layup. but all layups basically have to be whole layers

If its likely that you need some stiffness AND the part doesn't matter if slightly over size, put 1/8 foam in the middle of the layup to make the whole thing stiffer. Maybe throw sand on top of the whole work coverd in a plastic sheet to make a good bond.

That'll probably be too big and since the surface won;t be perfect anyway, just do the ordinary layup, let set up, and attach temporary stiffeners to the OUTSIDE of the layup w/ hot glue or best use spray expanding foam for a bunch of say 1x4s criss cross- then quick and no fitting and exact. pop the hood off from below(may be a bit of a struggle as the part is now stiff) and criss cross some foam half rounds on the bottom of your layup and glass those in for a stiff coffered subframe. pry/scrape/sand off the spray foam on the outside 1x4s and finish the surface like all of us poor suckers do here.

should work
-mick