Spray foam for travel trailer ceiling and walls?

The foam in the larger "kits" is better than the foam out a can. You will also have to clean up the framing and cut foam to install paneling back on to the frame. The spray is not without work, both in preparation and in final result.

I think you are a bit low in the estimated amount of foam needed. One thing, your ceiling cavity is not 2" at the center. Most trailers have a crown with up to a 6" cavity in the center.