Hi Rebecca,
You will probably find it difficult to pre-book sites in northern Italy for just one night in July (and August) because they do so much business. Having said that, if you just turn up early enough (before 3.00 p.m.) you will almost always get on.
No recommendations (other than use a good guide such as Alan Rogers) but at the risk of having this post pulled by the mods, one anti-recommendation. We once used a site that was mentioned in an overnight stay booklet published by Select Sites. To be fair, Select Sites did preface the whole booklet by saying that they did not endorse the sites because they had not inspected them - they were just recommendations from customers.
Well we arrived at this site about midday and found it a little downbeat but perfectly acceptable. You had to pay cash and hand over your passport. There were no marked pitches (we found out why later) but plenty of shade under trees. we were almost the only outfit there. As the day continued, more and more caravans, campers and tents arrived; and even a coach full of Japanese tourists which pulled an enourmous trailer in which they slept in coffin-like slots horizontally across it.
The inflow never stopped, and to cut a long story short we were knocked up by the owners at about 11:00 pm to ask us to move our car from alongside the van so that they could get another camper van in. It had to park so close to us that we couldn't fully open the door of the van! The whole site was an anarchic conglomeration of vans and campers with an average of about a metre between them. A big british outfit arrived about midnight and they tried to fit him onto the edge of the swimming pool. He refused. By one of life's coincidences we met up with him at reception of another site the following day and he told a story about how difficult it had been to get his passport and money back - it had taken ages of arguments and threats to call the police. The name of the site? Well so this dosn't get pulled by the Mods, I will just say that it thought itself to be International and was in Como.
Have a great time,
Mike A