Hi Mark,
Your in for a real treat, must have a word with my son and get him to treat me, Spa is an amazing circuit. We there in September to see the Spa 6hr Classic. As an alternative to camping have a look at the Holiday village at Domaine long Pre, Stavelot reasonably priced and a great place to go back to if it’s been a wet day, the weather at Spa is very unpredictable and I would take full waterproofs just in case.
A suggestion might be to see the Start of the race from the grandstands over locking the pits and then walk anti clockwise round the circuit, most of the paths are paved in concrete. There are some great places to view the racing, I particularly liked watching the racing at Bruxelles hair pin, the spectator area is on a raised bank over looking the track an offers a great place to take photographs.
Enjoy your trip
Dave