I am keen to talk to anyone with experience in making one off stuff out of fibreglass.
Items to be made are about 1500mm x 600mm and loosely described like a very shallow bathtub or better still a swimming pool with a shallow entry at one end 100mm depth at the deep end, in left and right versions.
I would be making the pattern and the 'plug' from surfboard foam (I guess)
You could make a closed mold and inject into it....... check out www.mirteq.com .
The attached pic shows calibrating wax being applied over a male mold, when finished I made a new female mold over it (replacing the one in the background).