Removing gray water tank insulation

Here’s the deal, I’m a person who’s inclined to repair rather than replace things. However, there are times when it’s better to end it rather than mend it, I feel that this is one of those times. The crack is about 18” long and runs along the edge of a channel located on the tank bottom. I have no doubt that if I removed the tank, turned it upside down, cleaned and sanded the surface, slathered the area with epoxy putty, and attached a plate over the cracked area using stainless steel sheet metal screws and fender washers slathered with epoxy it probably wouldn’t leak upon reinstallation. However, 40 gallons of water weighs 334lbs, plastic becomes brittle with age and the RV is going on 20 years old this year. I feel that rather than attempting to repair a 20 year old plastic tank that could conceivably hold as much as 334lbs of water, if I’m going to go through the trouble of removing the tank, now’s the time to spend the $350 (cost of tank and shipping from Tank Depot) for a new tank to replace it.

As I said earlier the fact that the front of the tank has several inches of polyurethane foam covering it and the RV bottom in that area is worrisome to me. I don't expect the hassle of laying on my back ripping out the insulation while it falls in my face will be a pleasant experience. Yes I’ll be wearing goggles and a dust mask, but that’s not a lot of fun either. What I’m looking for are tips on removing the foam insulation that’ll ease the process and possibly create less of a mess.