Any ideas for installing central heat in old OTR A/C ventilator compartments?

[Mex-Busnut]

These two factory OTR A/C ventilator compartments are approx. 3.5 feet long (in line with the walls) by 2.9 feet wide by about 18 inches deep. There is one on each side of the aisle. They are directly over the fuel tank. Both are accessible from outside. Maybe I could replace the lid with a screen or grate of some sort for breathing.

So: Do you think I could install an RV-type central heating unit in there?

Thanks in advance!