If you're spending more than a few thousand dollars on your mobile home purchase, it might be wise to invest in a purchase inspection, appraisal or online valuation report. I found this National Auto Dealers Association online too, but it does cost at least $20: http://www.nadaguides.com/Manufacture...
Another possible option would be to hire an indpendent, local RV mechanic or RV dealer to inspect and/or appraiser who's familiar with used RV values. You can find RV sales and service businesses on Angie's List (http://www.angieslist.com/rv-sales-an...). One tip that's applicable to both auto inspections and RV inspections: use your own pro, not someone the dealer or seller suggests.
If you're not yet an Angie's List member, you can use the promo code ANSWERS to receive 20 percent off a full year of local ratings and reviews for all kinds of home, auto, RV and health professionals in and around Austin.