Be thoughtful about it. Put a heater back in (just move it a little bit & use ducting surely? Put it on the floor for race car weight distribution if you like
) but run a few lengths of small ducting to key areas rather than heating up empty space.
Quite a few endurance cars at Le Man etc have started to run air conditioning & have been blowing air directly into the back of the seat via ducts, onto the pedal box, another one onto the steering wheel grip etc.