If it had that much dust on it the indoor storage area was obviously not a sealed building. I would do a complete inspection looking for rodent damage. Then you have to look at new batteries and ALL rubber components, seals, belts, shocks, gaskets, etc being dry rotted and ready to fail.
When I restored Classic Cars that were 50+ years old, the ones that were driven regularly were in much better shape than those that had sat for as little as 5 years, not running, in some indoor collection.
Only a very thorough inspection would be able to tell if this is a great buy or a money pit. Remember anything that you spend to make it roadworthy will not increase the value of the rig nor will any of it be recoverable.