I would not use the expanding foam, but if you do you can get 2 part foam in different densities

 

Well.. for the xB at least, using the wheel base of 98.4" for the est length of passenger compartment, 58.5" for height and 66.5" for width,
1 side = 5756.4" or 39.98sq ft figure 1/2 that is glass anyways so would probably be close to covering both driver and passenger sides.
rear hatch/trucnk is 66.5" x 58.5" = 3890.25 sq in or 27.02sq ft (again 1/2 is glass so other 1/2 could be used for firewall?)
floor or roof 66.5" x 98.4" = 6543.6 sq in. or 45.44 sq ft. .. unless you added a sun roof no need to account for glass.

for the legnth i used the wheel base as est
height i used total height - ground clearance
width nothin to account for.. (all measurements pulled from that official specs of the car)

ok.. that should cover the xB.. some1 else wanna tackle the xA or tC stats??