Heater placement

I am assuming you are putting in a heater with a blower and not just an infrared (radiant) heater.. if so, the main thing is to direct the air downward and get plenty of air movement everywhere. If the guy running the gas line is an HVAC guy, he may be able to give you some suggestions or ideas of what he has done or seen. You might also look into an "attic" furnace that would sit up above and then run some ductwork up there... but much simpler probably just to put a single box type heater on one corner....
I"m not one to talk, I have a big wood stove and 3 ceiling fans to move air around.

Insulation will help too!