That model Xplorer is a RVIA Type A, house built on a bare chassis. Frank Industries or successors also built Type B (van conversion) and Type C (house on cab chassis or cutaway) motorhomes with the same brand name.
Value on Xplorers gets tricky, NADA estimates don't always work. Xplorer motorhomes, the Type A particularly, are historically significant and were well made, factors that somewhat defy depreciation formulae used for book pricing. However, there is not yet the combination of scarcity and cult following that puts them into the investment grade collectible market we now see for RVs like early Airstreams or first generation VW camper vans.
Whether it is worth $8000 or $20,000 is going to depend on condition and your intentions. If you are buying it to use, it probably has less value than an example restored to original that you might be buying to hold for investment in hopes of appreciation in the collectibles market.
Right now, the 1960s models are collectible because of scarcity. I don't know that 1980s models are there yet.
