I will be driving from San Gimignano to Venice,i will be staying 3 nights. Where is the best and safest place to leave it there will be bags left in the car. We will be there in mid April.
I leave any bag I MUST leave laid open and in the covered trunk. Make sure your luggage is clearly visually comprised of underwear etc. Leave your glove compartment open, put a local paper (rumpled and turned to say the theater page) on the back seat, a copy of a local version of National Inquirer along with a roll of paper towels and a local bottle of water on the front seat. (Oh and throw a few candy wrappers on the floor....think about it...who does that except non tourists.) Additionally I use a bike lock cable to hook suitcases together and then to the trunk. The more of a pain it is the better for you and not the crooks. Of course your stuff may be all over the ground but hey! it's washable right.
Nowhere is 100% safe in Venice for parking. You might enquire with your hotel. Most tourist lv their car at high rise Tronchetto at train station area. But there have been problems with break ins. Hide everything and try and make your car look like a locals. Alot of travelers have this dilema.
If you're going to park right in Venice at Piazzale Roma, it's very safe. In fact most floors have an attendant on duty 24/7. I'll admit it' sa bit unnerving the first time you do it because you have to leave your keys with the attendant but I've done it at least 20 times and never had a problem. I actually prefer doing it now as I believe it's safer. Only drawback to parking right in Venice is that it's expensive (about 24 euro for 24 hours). You can park over the water in Mestre a lot cheaper but I can't vouch for how secure it is. If it makes you feel any better, I've been parking in Venice for more than 10 years now and have never, ever had a break in or any other problems.
But Rik, you are not a tourist and you most likely do not leave luggage in your car.
We left our car in the parking garage across from the train station in Mestre. We retreived it and drove on to Varenna. It was there that DH discovered he'd left his daypack in the garage on the floor in front of the car. That's why four adults didn't see it when we drove off - or maybe it was just our stunnedness. His camera/attachments;running gear/guidebooks/ipod/etc. were all in the bag. He phoned the garage from Varenna - no mean feat when you are uni-lingual and not in Italian - and the fellow said the daypack had been turned in. We all assumed the camera/ipod would be long gone but DH needed his running stuff so he drove all the way back to Venice to get it.........yeah, he did. EVERYTHING was just as he'd left it. We figure the smell of his unwashed running stuff was enough to stop anyone from delving deeper - lol! But really, it was the honesty of the finder and the attendant that was so impressive. Don't think that would have happened in our hometown.
Lola, assuming the bags are in the trunk, I'm not sure how that's relevant as locals don't use the tourist parking garages so pretty everyone who parks there is a tourist...however, there have been times when we've stayed overnight and the next morning, dropped the bags off at the car while we walked around the rest of the day. I've also got plenty of crap in my car such as CDs and stuff which I don't always remember to put in the trunk. That's why I prefer the floors where they have an attendant, they are much safer.
I left our rental at the Tronchetto parking garage. It is about 24 euros for 24 hours. If you are staying at a hotel ask if they have a discount coupon. For a little extra per day they have a secured parking area. It looks like a jail cell for cars. I also noticed that some of the locals park their cars there for weeks on end. I did not see any evidence of broken glass anywhere on the ground. IMO, if the vehicle has a trunk, i would not worry to much about it. Our Citroen C3 Picasso was a hatch with a cover that did not cover the trunk. There are also much better vehicles parked there than the cheapie we had so I thought my odds were pretty good.