Greetings & Welcome!
I like to start with a cheap used generator, to which I add a quiet muffler. Then I have all the portable power I need, for whatever I need it for.
Due to my build philosophy, I rarely need power tools, but a drill/screwdriver, and a jigsaw can handle almost everything. Toss in a hand file & some sandpaper for good measure, and I could build a camper you’d swear was done by professionals.
That being said, I prefer to NOT build anything in. I like to do it more like a normal house, simply move my furniture in and secure it. If I start with a passenger vehicle, like a passenger van or shuttle bus, the floor, walls, ceilings, & windows are already in & finished, saving a lot of time, money, & headaches, and lots of opening windows are what makes for a much more comfortable home.
Portable, modular builds can be easily reconfigured as desired. The same can’t be said for built ins… My “No Build” conversions can typically be done in a day and livable by bedtime.
Starting with a cargo van or box truck, most people spend the time & money to add windows, and do the floor/walls/ceiling. All of which are poor choices, and to only wind up with an inferior camper.
Many commercial vehicles are geared for hauling heavy loads in town, not highway travel. The result is worse gas mileage and more maintenance required. Make sure you get something geared for highway miles, or be prepared to spend the money to convert it.
Pre-computerized vehicles are much more reliable, require far less maintenance, and can be to tuned to get far better gas mileage. Newer isn’t always better, just more expensive and more headaches.
Both my bus & my van are 1973 models, pre-smog, and pre-computer, totally reliable, low maintenance, and drive like a dream.
"Failures are merely a learning oportunity." ~ Rubber Tramp