Good deal! Worst case scenario you can use it as an aluminum shed.
I picked up my 77 Sovereign
for $800. It looks in similar condition to yours, only my interior was mostly gutted. It had a 2 year old AC unit, newer Iota Converter, water pump and usable water heater, all DC and AC functional. 3 years later (not working on it on a regular basis)... and around $4500 in total spent It is almost a functional rolling aluminum tent.
For $500 it is worth it, if you have the time and money to bring it back to life.
Good luck on your new addiction.