Just bought a used truck and used 5th wheel. I prefer someone else take the big hit on depreciation. Both were from dealerships, but I looked at private sales as well.
Zero in on what you're looking for. The internet makes doing your homework vastly easier. I set up a spreadsheet and tracked truck and FW makes/models for the better part of a year to know the selling ranges was for each. Read forums for suggestions, such as above, for what to look out for and what items are deal killers; e.g. stained ceiling in closet.
Take your time and enjoy the process.