What about putting the window decal on a cast off piece of Lexan, then sticking that Lexan somewhow to the window using a nonpermanent adhesive? It would be a lot easier to get off. For other places on the RV, maybe stick those on a white piece of plastic that is attached via Command adhesive as well? I would also consider using four Zip-ties and having the plastic be mounted between two latter slats, where it is obvious, but easily removable.
I'm with R2D1. Maybe my tinfoil hat is showing, but I don't like stickers in any way, shape, or form. They attract attention, and I am concerned that it would be unwanted attention.