I'm building a radiator cover/window seat. I only have about 2" between the radiator and the wall though. Can I use some type of material (wood, metal, etc) placed ON the radiator itself for bracing? Which material would be suggested (due to the heat of the radiator)? OR, is there a better way? Thanks in advance!

There is some decent gauge aluminum angle stock that would work well, you can find it in the Depot for example. That way it's easier to drill for the studs & self tapping screws for the ply.

Radiators aren't combustible, but still make it vents well.