Taffy, David is right about Innsbruck you need at least 2 or 3 nights there and we have not found a problem with the Brenner Motorway with an 8 metre caravan.
With regards to Bitburg that is our first stop, a site just outside at Oberweis 5 star, 15 euros per night on ACSI Camping Card named Prumtal Camping. We then usually go and spend 3/4 nights in the Black Forest at Bad Rippoldsau, Camping Alisehof 5 star with ACSI Camping card again and then Camping Nattersee which is another 5 star Camping Card site all 15 euros a night but you would have to check prices in July. We have done this trip quite a few times and love it.