I booked the Bella Italia for this June last week - I found it best to contact them directly - and yes availablity is very tight; but having spoken to people who have been there before, it seems like a very good deal... despite the fact we had to go for a 6 person apartment even though theirs just two of us!!
From my own research, stay clear of any sites not located on the south coast of the lake unless you plan to drive, as the bus services stop very early heading north (whereas the south coast is linked by rail to verona/milan and has more nightlife). I kmow you are renting a car, so this mightent be an issue for u... but for day trips to verona/milan it is much easier to walk out of campsite and hop on the very cheap and frequent train rather than spend a fortune driving into big cities and looking for parking.
I've been to garda last year, and cant wait to go back! Brilliant place!!! Themepark is excellent, food is fabulous, verona is magic and people are very friendly... oh and the lake is something special!!!
As for hotels... they are very expensive, even the rubbish ones, it might be worth staying in a (cheaper) hotel a few miles from the lake (in Verona/Brescia) for the first few nights and then going for bella therafter. Again, ring Bella or email them directly - dont bother with the tour companies/canvas/keycamp - they are dearer and are unable to tell you exact details - ring bella! They actually rang me after I made my booking to tell me to book an extra night to take advantage of a 7=5nt deal! Not often people ring you after a booking to convince you to hand over LESS money!