I just bought a 2001 Gillig 35' Low Floor on Friday. Not sure if the one you're looking at is a Low Floor Advantage or a Phantom. Anyway, they seem to becoming available recently. Mine has 463,000 miles on it and I just drove it 700 miles without issue. With new tires (mine have no tread left) I would drive it across country in its current condition without hesitation. It has air suspension and floats like a dream down the highway.
Not sure what you want to do with it, but if it is a low floor, you will have no under storage. However, the front has 8' foot ceiling and the rear has 8'6" ceilings. And they are wider than a school-bus and have 8'1" interior with.
Gilligs have a stainless frame and fiberglass body, so rust is not a problem.
This was an online auction, there were 10 Gilligs, the highest sold for around $1600.00. I got mine for $1430.00 which included the buyers premium (10%).