FoamBoard Walls

[DR2M]

So just casually strolling the dollar store grabbing a poster for school when I found this foam board (Readi-Board is the name) for a dollar. I picked up two thinking I’d use them as walls for a tank. I’m setting up for a BP I’m hoping to get soon for a show in a few weeks. I just have a few question if anyone has attempted it. I know some people use spray-foam insulator (I think) to make Hides and custom backgrounds.
1.) Is this safe for the BP?
2.) Is there anything I need to specifically worry about when doing this? (Water, heat, etc)
3.) Opinions on substitutes that could be a better use than this. (Relatively cheap)

In addition to this, Who anyone use spray-foam to make custom hides for a BP? I just like to make things myself, makes the experience feel better personally.

Thanks in advance.