We have a dometic, 13500 btu. It's a standard profile, not the low profile. We were advised by the svc mgr at camping world, (who installed it in less than 2 hrs) that this model was the model on 98% of the campers and rv's they sell, and they would have parts for this one on hand at any camping world. Ours is 4 years old and will still freeze us out when it's 100+ outside, I would not even mess with heat in your roof unit. I would go with a fuel fired heater. Roof air units need 2500-3000 watts to run, so just about APU ought to run it reliably. We run a Proheat APU with over 18000 miles on it and it works just fine. Although I wouldn't give up your fantastic vent. Guess you could have just called me and asked me.....