Hi Gayle; Welcome to Permies!
Asking questions about your concerns is not silly at all. 72' is just more than you can push the hot air. If you tried to run the lenghth of your trailer (just 50') I think you would be disapointed in the back bedrooms.
I suggest 2 rmh's , one at the bed rooms and one in the living room. It is twice the work to build but I think you would be much happier and warmer.
A Rmh does not have to be huge if your not trying to heat the entire 72' . As far as masonry bells, the brick will not seep CO/2 thru. But if that is a concern in your eyes, (no matter what anybody else says) then you can cob the inside of the bricks with a skin of mud. That would effectively seal even your joints between bricks. A different style of stratification chamber uses 55 gal drums split lengthwise and set end to end. Those barrels are then encased with brick and covered in cob. No chance of any CO/2 escaping thru solid metal. (Known as the Matt Walker 1/2 barrel bench)
My suggestion is for you to build a conventional rmh with bench in your living room and to build a smaller brick bell rmh in your bedroom (you may as well benefit the most) Check out this post...
https://permies.com/t/43809/Masonry-stove-diy-build-feasible This size would be just right for your bedroom. The poster built a batchbox style but it could be a J tube
feed instead. She built a 4" which is smaller than recommended , a 6" is what I recommend for your bedroom and I suggest building an 8" for your living room. Not that I think you need an 8" it just that an 8" burns longer , is easier to reach in to clean
ash, allows using slightly larger
wood as well.
Do you have a copy of the RMH builder guide ? It is the go to book for any new rmh builder. It is available from amazon or from Ernie & Erica Wisner directly. They are 2 of the top rmh builders/ innovators with over a 1000 builds to their credit. A can't recommend this book
enough !