Tip of the week:
Insulation is a bigger friend than you could possibly imagine!
Thermal mass takes time to release its stored heat, so every day the battle must be fought, unlike a refrigerator which stays closed most of the time. (We don't bring everything to 72 degrees every day, but on these unite we expect to.) It is not that the units are bad in and of themselves, but we are asking a lot from them.
For me it has become a balancing act. Make a list of all the variables and you will understand what I mean. I have a Peliter unit on a chamber about the size of a 20+ gal tank. A LOT depends on ambient temps.
And Insulate! Insulate! Insulate! And then Insulate some more!
If you add enough insulation until it looks bulky and ugly, and then add more!... you will be close to the amount you are gonna need! (Like people are finally finding out with insulation, it saves a lot of energy and makes up for its cost in no time!)
Av, lots of time, study, experiments and effort and that's all I have for you right now!
By the way, what is your motivation for this project?
Hope some of this helps!
Paul