Filling in cracks on both of my 33 ft Class A and 5'ver will take 2-4 tubes. IMO people use way too much which just leads to issues down the road, or for the next guy.
For me, I clean the area well and make sure it is dry (overnight.) Working in 2-3 foot sections I apply a bead of Dicor. Using a plastic spoon or my finger I smooth it out over the cracked stuff to speed up the leveling process. 24 hours later everything is nice and pretty.
Thereโs no fool, like an old fool.