I use a lot of expanding foam......it's the cat's ***, IMO.
Clean up is easy with lacquer thinner......even the applicator nozzle (tho Not on your foam) but have some paper towels standing by for wipes of spillage. I coat the stuff with light weight spackling compound (suitably thinned for workability). The LWSP is not very stout but it sands & shapes easily (but you don't want the dust in your nose).
The best EF is the windows/doors stuff. *Mostly* it sets up at around 3X the applied size and free of voids.
Wanna build a mountain? Lay down a blob of EF. Let it set for a couple hours, lay down another blob....keep going till you reach the ceiling, let the whole works set up for 24 hrs. cut to shape with a roughly sharpened knife (bench grinder/decent file is gud). The EX IS compatible with blue, pink, & white foam and WON'T push your layout apart

. Save your EF drop from cutting.
Great for undulations in flat surfaces....just glue it down & carve.
5-7 bucks a can at about any hardware store.