I'll try to answer your Q's...
#2- Wood Veneer
#3- Have had mine for over 2 years and have no problems with the belly. The trailers belly that is, my belly is a different story.
#4- Not that I am aware of and I did not see it on the "Options" list.
#5- Optional is the Deluxe porcelain toilet upgrade
#6- No
#7- Exterior walls R-9, Roof R-14, Floor R-21
Most all of the above info can be found at the
Montana Website
Look at the Construction, Standards, Options and Specifications listed in the left column on the Home Page