I hope we're not hijacking this thread.
pp - Do you mind sharing the heaters' make/model?
When we purchased the bus a little over 5 years ago (we had a fiver before that and have been fulltime RVers for more than 14 years) it had Platinum Cat heaters installed complete with venting and thermostats. We loved the efficiency of them, but alas, they wore out (26 yrs old) and I couldn't patch them back together anymore without new parts. Getting new ones isn't an option, though I can't understand why no one has started manufacturing them again. So last year, after doing lots of research, we decided the best approach both asthetically and efficiently was to replace the Plat Cats with another catilytic that fit the same cutouts (close enough anyway). We settled on Olympian Waves-2 size #6 and 1 size #3(bathroom). They connected to the existing gas lines and fit over the original cutouts with little modifications. We use the existing 2" pipe exhaust vents in the rear for feeding them fresh air in addition to the three open roof vents. We had to add the Maxair vent cover to keep rain and such out of the kitchen vent because it's just your standard crank open style with fan, BTW. The bedroom is a T-5 fan assembly that doesn't seal unless you manually attach the inside cover. The only drawback is that they aren't thermostatically controlled like the Plat Cats. But they're a lot quieter than the Plats because they don't have an exhaust fan. Our windows are not full of condensation unless the wife is cooking spaghetti or some such. And the fuel consumption I stated in my other post included cooking (we heat a lot of water for tea) and using the oven twice (before it quit). We have 2 CO detectors, one in the bedroom by our heads and one in the hallway near the floor. The Olympians are supposed to shut down in the event of low Oxygen or flameout, but redundancy is always good.
Hope this helps, Will