I used Snow Roof's Elastometric on the Class C (roof coating, "tape"& primer) works wonders and no more leaks on the roof. Lowered the summer temps quite a bit. Down side is I have a "dip" towards the rear and Snow Roof doesn't like standing water (ponding is what they call it). So if you have a flat roof, you need to watch for that. I did the roof in 2006 or 2007 and had to have the primer ordered in.
For the skoolie (rounded roof, no standing water) we used Henry's Solar-flex
from Home Depot
. I used the "tape" I had left over from doing the Class C and embedded it into the Henry's to seal leaks. Then put two coats of roof coating on the roof. Really needed three coats but it was too hot. Henry's makes a clear elastometric caulk
that you can use to seal leaks with (I have bought several tubes at Home Depot
. Apply on WET or dry surfaces. The large 4.75 gallon bucket will cover a 40 ft bus with 3 coats. I used a paint roller.