David & I stealth converted our bus while living in it. It's not a method I recommend unless you have no other choice.
We had used the bus as a cheap moving van to get one of my daughters (Das Mel on this forum) out to NM to be with her twin sister.
We did the most obvious part, the exterior, in the back yard of one of my daughters (the one who didn't like the bus). She was only a few blocks away from where David was vending food so I could walk there for lunch or if I needed the Jeep. The house was only a mile or so from the RV park we were living in (Class C). We pulled windows, rebuilt them, skinned over what we didn't want, fixed roof leaks and potential roof leaks, coated the roof, painted the exterior, turned the two piece door into a one piece door, got all the exterior lights cleaned and re-installed, basically all the exterior stuff. Plus we cut a hole in the floor for a future hydronic heater. It was a very noisy, messy and smelly procedure so it was something we wanted done while all the windows were out and the place was a mess anyway.
Then we did the bare bones stuff needed for us to be able to live in it or what I call a "metal tent" conversion. We had an RV toilet (since replaced with a residential toilet), cold running water in the bathroom sink only, black holding tank installed, fresh water tank and my filter setup installed, drains and agricultural ball valves (not RV bayonet valves) on the drains. Used the C5 Christmas tree lights for lights, hooked up the refrigerators (I have two undercounters), the freezer got loaded back on the bus (it was Das Mels' first major appliance purchase so we had to keep it in the family), my old LP gas range from my last house, an old glass topped rock maple table I've had since it was bought in a thrift store back in the late 60's flanked by two RV chairs we got off of craigslist, my cedar chest David made me as a wedding present, our old king sized 4 poster waterbed frame that we cut down to hold a full sized air mattress. Forgot, we cut down a vintage 1926 craftsman oak fireplace mantle and mounted the TV to the area where the mirror was. Stuck a long folding table (like a school cafeteria table) in as workspace for the kitchen. Packed the clothes into boxes and the hanging stuff went on a wooden rod held up with metal shelf/pole brackets. That took from about the end of May 2011 to the beginning of November 2011 (roughly 4 months plus a week or two)and we moved into the bus the day we headed to Roswell in the bus Dec 10, 2011. We were delayed a couple weeks due to winter storms, one of which shut down I-25 and both shut down US380. Our only heat was an electric space heater (we soon added an extra heater) and we operated the whole bus off of heavy duty extension cords that we used to use in our construction work. Those same cords eventually ended up in the walls as our interior wiring.
We pulled the "finished" bus into an RV park that had a bathhouse and laundry facilities. We are lucky in that the park we are in had a lot of workers and are a bit more relaxed about noise than the typical RVers. We do try to keep it very quite. But we do run battery operated circular saws (both side the bus and outside the bus) as well as having run a wet saw in the shower stall when we installed the tile on the kitchen counters. We only worked during the daytime (not too early and not too late) and tried to keep the saw use down.
We often had sheets of plywood ripped down into more manageable pieces (2X4) at Home Depot or cut them ourselves in the parking lot with the battery powered circular saw (Hard to put a 4X8 sheet of anything in a Jeep). We used hollow core doors for our partition walls so we only needed to cut the curve to fit the roof and had an instant finished wall. Saved a lot of time and noise.
We tried to not leave anything out that showed that we were "remodeling" the bus. We also had to rethink a few things as well. Doable? Yes. Easy? No. And I'm still working on it. But it's way past the metal tent stage.