I am putting a new cover on one of my boxes here shortly as well.
Friends don't let friends use ethafoam. The way I roll is that you aren't my enemy so you must be my friend. Don't do it.
I the last couple of times I have gone to the pool supply and used their 1/2" smooth surfaced, closed cell foam. The floaty stuff that after you take the big ole cover off a hot tub there will often be these sitting on the water.
It works great. Dries quickly after a swipe and I get mine pretty cheap cuz its leftovers from the bigger jobs. I use this in the bottom of my dry boxes too - so I can drop my whisky bottle in without fear of breakage.
To apply it I use regular huffing type contact cement ( the water based stuff sucked when I tried it so go for the nasty shit). I have a buddy who swears the Super 77 3m spray is all he used. Double passes on both box and foam. If you use that I would test on a small piece. Good luck.