If you are going to invest time and money into this project, do it right and take down those inner skins. It will make you a better busman, you'll know your bus better, and you'll get a better end result and it only costs you sweat and some phillips bits.
I used an an angle grinder to cut x's in the head of my rivets and then chiseled them off with the chisel attachement on the end of a pneumatic hammer. Some people also call this an air-chisel.
You can do it with a cold chisel (a chisel made of hardened steel meant for this, not a wood chisel) and a heavy hammer instead. I did i this way once, and vowed never to do it again. You can find used air hammers/chisels for 30-40 bucks. Worth it if you have a compressor. I also used a die grinder and pneumatic nail gun-16 gauge for most general carpentry. Other than that, I used my cordless drill and cordless impact driver the most. Followed by a table saw, sliding double bevel compound miter saw, angle grinder, welder, and jigsaw. I can build just about anything. I'd love to have a drill press and bandsaw.
Im going to also strongly suggest not using rockwool. If you are going to live in the bus, you will really want it to be as airtight and sealed up as possible. Foam has too many advantages over everything else to not use it. If you can't afford it, save up. Ive built buses without spray foam and regret them. The two I have sprayed feel like a home when you step in.
Rockwool may perform better than fiberglass for water absorption, but still absorbs water and cant hold a candle to what sprayed in foam does--which is not get wet in the first place. It also has about 1/2 the rvalue per inch of spray foam. BOOYA!
I just spray foamed a short bus Im building today and the results, again, are incredible.
It instantly evens out the high and low temps, dampens sound, adds structural rigidty, and seals the bus. Can you tell I drank the spray foam coolaid?
Anyway rock on man, don't get overwhelmed. If you werent going to learn anything on this project, why would you even embark on it?!
Patina enthusiast and professional busman