Campsites for "campers" in Florence
Ciao Ginny,
How many days are you planning to stay in Florence? If you're just looking for day parking large enough for your motor home, you will find plenty of space around the stadium area of Campo di Marte. Many of the buses that bring tourists into Florence park in this area, so you won't be alone

. From here you can easily walk into the center or even catch a city ATAF bus.
You will also find large enough parking spaces along the Lungarno della Zecca Vecchia or in the area around the Cascine Park on other end of the historical center (map both on Google to see where they are located). These are just for parking during the day. In any case, avoid entering the "ZTL" or limited traffic area in Florence's historical center. Aside from high fines if you don't have a permit to enter, the streets are often one-way and are narrow so you'll likely have problems with a motor home.
If you're looking for a campsite to be able to have water and electricity hookups as well as waste water disposal, then the most popular one is right under
Piazzale Michelangelo. Very central, close to all the sights. See their site for more info and costs
http://www.ecvacanze.it/en/elite_family/tuscany/camping-michelangelo
Then there is the one right next to the youth hotel at
Villa Camerata. Wasn't able to find an official site but you can see some of the info on it at this site:
http://www.ostellionline.org/ostello.php?idostello=188
Just above Florence, in Fiesole, you'll find another campsite, the
Camping Panoramico Fiesole, that offers "camper" services (which is how "motor home" often gets translated into Italian but you'll also see "caravan" used). This one has two other campgrounds in the area around Florence, one to the north in Mugello and one in Bottai right outside Florence near the Certosa A1 exit. See their site for more info:
http://www.florencecamping.com/
Still within Florence is another one called
Oasi del Camper in southwestern Florence -
http://areadisostafirenze.com/ that also offers water and electricity hookups.
The last one I found is
Il Poggetto which is further away from Florence but not too far, quite close to the A1 but easier to get to if you're coming from Rome. Il Poggetto seems to offer a wide range of services as a whole. See their site:
http://www.campingilpoggetto.com/
Hope these suggestions are useful in planning your trip to Florence

.