flya750, the OP might not have known that there are glassed in wooden supports for a heater just forward of the driver's seat under the bow deck. I probably wouldn't have known that had I not removed the broken heater from my '87.
That said, I am worried about hanging my new replacement heater from the same slats because they are rather thin and the new unit is heavier; I'm concerned that I'll upgrade to a larger screw which would promptly puncture my deck. That's my nightmare.
I am considering securing some thicker StarBoard type material in a similar location before mounting my heater. The OEM heater mounting screws in my '87 were puny.