I drove around Tuscany, Umbria and Marche for 5 months last year. I didn't stay in cities much and drove about 12,000 Kms which included getting there from Ireland. When driving through Germany I picked up a book on over 7,000 "Stellplatze" throughout Europe. They are in almost every popular area and cost from free to about 18 euros if they include electricity and have a few showers. I found that when one is approaching a city these parking places almost always have a site close to a bus stop or the escalators to hill towns. I especially liked the one at Volterra that cost 8 euros for 24 hours and had steps up to the town. I am in Thailand for the winter and don't have my book with me to give you the author's name as I am sure that it is available also in English. It is easy to understand with pictures of each site and led me to many wild camping spots.
A favourite campsite on Lake Trasimeno is at Castiglione del Lago named Campeggio Listre. It is directly on the lake and does not have fancy pools or large restaurants but it is a family place, most friendly with good toilets and showers and so very cheap. I was alone so it was only 9 euros. Many people go back there again and again. Most convenient for going to Cortona, Pienza, Montepulciano etc. Great cantina's for wine all around this region.
email me if you have any questions. I especially loved Greve in Chianti, Bolsena on the lake of the same name - a great little town with a camp site at the lake for 15 euros/night, simple but walking distance to town along the lake and has electricity etc. This was in high season when everywhere else was just too much money. You may not want any camp sites but just letting you know a few of the rustic ones in case you're interested.
Aileen. email a.roantree@+++++.com