I would respectfully disagree with artistic Adam, and I would cut the doors out before epoxying the inside. yes, depending on the saw you use to cut the doors out, there might be some minor tearout, but getting in and out of the camper before the doors are cut is an exercise!
as for minimizing tearout–I bought a Dremel ultra-saw. it is designed like a miniature old-school Skil worm-drive circular saw. the blade (actually its more like an abrasive disk) is mounted forward and you can easily see the cut as you are making it. plus, you can set the front of the shoe on the work, and then carefully plunge the blade into the wood. I was able to hit the cut line dead-on on all the cuts. it makes a lot of fine dust so wear your dust mask.