How do i deal with XPS foam texture and softness?

[wispy egret]

Hi! I bought a sheet of XPS foam for building terrain and i'm trying it out on a small base right now. What i don't understand is how people get rid of the foam texture to make it smooth (see image) and how do i make it firm (so it can't get easily dented after i'm done). I don't have a product like Mod Podge available where i'm at, i tried PVA glue but the foam just soaks it in and barely makes a difference even after multple layers. I can imagine the paint will be soaked as well.

Thanks, i'm getting a little desperate :/

[vernal oar]

All you can do is coat it in something else

like white wood filler

coat it, sand it, coat it again, sand it again

til it's smooth