Like everyone else said, fix the house batteries first. They also power the starter on the generator.
The Chevy chassis could have either disc or drums in the back depending on how big it is and how it's configured. My 30-footer has the bigger 19.5" wheels and 4-wheel discs. But some had drums, too. Smaller ones (under 30 feet) had 16" wheels and drums. You can easily see which you have through the holes in the wheels. Discs are easy, drums a bit harder. It's probably a P-30 chassis.
As far as value goes, it's all in the enjoyment you get out of it. You have a money pit now. If it needs tires, the value is close to zero.