I shall be leaving on Sunday for Spa as I'm marshalling there again, at Post 12 which is Pouhon, and as already mentioned is an excellent specy spot. If you camp at Les Combes then you can walk under the track to the huge bank where theres loads of space but get there early as it soon fills up.
Along with Monza this is my favourite circuit, I firts went to the GP there in 1970 which was the last on the old circuit won by Pedro Rodriguez in the BRM. I've been working there now for the last 20yrs and haven't missed a GP since.
If you get time then trace the old circuit as it's still possible to drive round most of it , have a look at the bottom corner at Stavelot where the 917's were taking at over 175mph and stayed in top gear from Les Combes to La Source, over 7.5mls!!
I hope you enjoy it but expect to get wet !!