Electrical and plumbing .
Electrical is standard house wiring for the 120 volt, you can get those most anywhere (Lowes, home Depot, Joe's hardware). and even plumbing parts the faucets and fixtures may be found at the bigger Hardware sources, pipes are usually PEX which Home Depot has a version of (likely Lowes too) but other options may be usable.
That leaves walls,, Plywood. and paneling work well there,,, On the aobve list change "joe's hardware" to Peat's Plywood, or Larry's Lumberyeard" (All generic names by the way intended to represent the name of your local Hardware or lumber/panel store).
Windows may be the only tricky stuff, Windows and doors are typically RV, not Homeowner. products.. And there you need a bigger RV store, salvage yard, parts store or Camping World.
Home is where I park it!