What do you use to cut off the excess?
An electric fillet/bread knife easily makes nice straight cuts in all kinds of foam. Spray foam to that stuff they put in hard-side gun/bow cases.
Danny said the hairspray worked,
the woman said it works on a lot of stuff.
I tried it on Sharpie our daughter used on the new, white, refrigerator🤬🤬!
It took it mostly off. Better than anything else we tried.
Rubbing Alcohol works great to remove "sharpie", at least it does to remove it from plastic MTM ammo boxes. Put the alcohol on a cotton-ball, Q-tip, or a rag and the Sharpie just melts right off.
