Being unable to heat my van over night, I did try once to insulate it and tbh it had very little effect.
Heat has to be present for the insulation to retain it and even then I think the insulation would have to be fairly sustantial and thorough.
So I took a different approach, being a simple diy system without an onboard ro, it was easier to isolate tank and drain system down on cold nights. I mounted pump and controller on a board thats quick release so can be taken in at night and a van mounted removeable hose reel, my situation does not really require anything else even if we have a cold winter.