My mobile home's floor joists are insulated throughout with 6" fiberglass batts held up by some kind of steel threaded and webbed, breathable plastic. The mobile home sits on cinder blocks (2 blocks high) which in turn sit on a cement pad foundation (8"x24"). Someone built an 8'x16' addition onto the home and removed 4' of the cynderblocking under the 16' wall where the addition meets the home probably to allow for air and heating. They did not insulate the addition floor joists. Instead, they insulated the 3 exposed perimeter pony walls of the additon. There is no heating under the home. So, I've got insulated floor joists throughout the home's 14'x70' dimensions and 3 insulated pony walls on the additon, meaning, there is no insulating value in the floor area of the addition.

Should I insulate the whole cinderblock foundation to match the 3 pony walls and add heat, or should I crawl under the foundation and add 6" inch insulation to the additon's floor joits to match the home's and continue not heating under any of the foundation?