Kitedemon, you and serpant merchant were a huge help when I converted my yeild Beardie cage for my first and what I thought would be my only ball. LOL!
It worked out perfectly! Now that cage will be passd on to my little cousin this summer. The more. I think about it and monitor my room temps the more I think it will work just fine. I think the doors may have to be there because that is where the long side of the tub is but the doors won't be air tight and I will have some vents on the doors and maybe even the back if needed. I will probably build it first and see how temps etc are and then install vents slowly. Lather rinse repeat until it works out. Who knows, the front doors may have really large vents. I don't think it will be too difficult to raise ambients up 8-10f. I actually think the large PVC enclosures I was thinking about would have been slightly more challenging because it is a much larger volume of air.
BTW I think the water heating system is a great idea! The only downfall (like liquid cooling for computers) is the possible leak factor but with careful installation I think it would be a great heat source and really efficient. Especially if you use a rad of some sort you could cover the whole back of a rack with a nice gentle heat.
The deep blue LED rope light or light strips may be another way to help the ambients. Also it could create a nice look. I use it in my current setup and it is always warm. That little bit of heat would add up in a small space.
Always a pleasure chatting about design. I have poured through old threads looking for similar situations. I think I over think things before I start building but I haven had any failures yet (knock on wood).
Thanks again.
I will post a build log when I start with posted temp results. I wasn't the first with this situation and I won't be the last.