Heat Loss when bunk end down?

Hello. I'm new to forum. I'm presently an experienced popup camper.

   I'm taking a really hard look at Rpods, in particular, the 176T.

   I have a somewhat odd question. As you probably know, in a pup, if it's 40 degrees outside, it's 40 degrees inside.  We have an onboard heater, but never run heater overnight.

   Has anyone noticed if Rpod models with bunk ends retain heat with the bunk end open. Because there is only one bunk end, and the rest of the unit is hardsided, I thought it might be that the unit stays relatively warm. Or, maybe with the bunk end open, it's like opening a door to the outside.

   I'm asking as staying warm is one of the major reasons for looking at a small TT. I realize that the unit can be slept in with the bunk end closed too.

Thanks.

   Modifying Post: Thanks for responses so far. To be clear, there are two of us camping.  Most of our camping is in national parks, without hookups, so we will not use heaters for sleeping as we'll only have enough battery power for taking off the morning chill. I refuse to camp with a generator, but have solar panels (that can only do so much).  We're interested in the 176T because the slideout gives more room on the floor.
  Space is a major trade in considering an Rpod. I have a 12 foot pup, with slideout dinette. It has 12 foot of totally unobstructed 'hallway' and is 25 feet long with bunk ends opened. No small trailer gives us that kind of space.

IF it's just YOU, then  I wouldn't want the a T-model, more to mess with.   A 172 gives you the most enclosed sleeping area, 2 42X74 bunks, plus the 58X74 queen dinette (171 is second).   Several owners use the Top bunk as storage, sleep in the bottom and leave the dinnette up.   The Pod heat works well, but so does a small cermic heater.  I've NEVER been cold in Podterfly, but then I haven't taken her very far North,  but I do remember a post last year where someone got snowed in and he seem to be happy about the r-pod performance.

Thanks for response. I'm only concerned with heat retention. Heater would only be used 1-2 hours a day, at best. A popup, when using heater, stays warm about 20 minutes. I was hoping the Rpod wouldn't lose temperature as quickly. As I modified my original posting, we dry camp so trying to retain heat is a question for considering the rpod.  

I would think that the T models will lose heat not as rapidly as a pup but nearly so (like the open door) If you are concerned about moving space you might want to look at the 175 or 177 with the slides. We have a 175 and it retains the heat rather nicely most of the night. We can dry camp with heat using to warm the pod up before bed and in the AM in the fall for a week. Mind that is not using the water heater and using lights sparingly. We do change the propane tank once. There is enough space to get around each other easily although it does get a little crowded when the 100 lb dog is added to the mix and want to be in the middle of everything.