You may want to rethink this. Camper siding is nothing like house siding. Camper siding fits together from the top down. House fits together from the bottom up. Camper siding us help on with 10,000 little 1/4 staples. (not a real number, but there will be plenty to pull out). All of the staples need to be removed. If you are talking about siding that is very long, it will take several people to remove and replace. It is very thin, and if you let it bend, is is no good anymore. You will need these people for the removal, to save the old siding, and the install, to help with the new siding. It will be shipped in a wooden crate, and must come by truck, so you will need friends to help unload, because the driver won't. You need a flat, level place to work, and scaffolding preferred, as you will get tired of moving ladders, and everybody will need to be up at once removing the higher siding and not letting it bend.
As for the window, once you have it removed, put the new siding on, don't worry about the window, cut it out later by drilling markers from the inside. Be careful, and don't push the drill too hard.
You will also need a big tarp to cover everything, in case of rain.
Lastly, what caused the damage, and are you sure it is just the siding, and you won't find cracked studs when you get in there, and or a damaged roof?
One last thought, check and make sure the guy trying to sell, didn't turn it in to his insurance and that they "totaled" the camper. If so, you will have a salvage title. May not matter to you, but it will if you ever try to sell it, and you may not can insure it.
Sorry for so long, and good luck.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT