You will quickly discover the economy in used is limited. It's nice when you can find the right thing at a reduced price but along with that is the time invested finding it, cost retrieving or shipping it, then more time and money fitting it for your purpose. So while I wouldn't advocate all new as a default, careful what you invest in finding used, it may end up costing more than new when you're done. My take on it would be rather than seeking out the piece parts, maybe find a derelict RV you can buy whole and part it out. One with water or collision damage would be very inexpensive and would yield a lot of usable house parts. I've seen some limited selection of RV usable items at fleamarkets and thrift stores, so making a pass through those once in a while might turn up a few items (along with some entertainment value).
Mark B.
Albuquerque, NM