Safe parking in Rouen?

I should not project American practices onto France, but every fully-attended (i.e. valet) commercial garage (indoor parking) I've ever used in the USA has included on the ticket, a waiver for any removable attachment or contents of the car. It seems unlikely that you can rely on another country's laws to protect you better than that. I understand that an attended lot is safer, but I've mostly experienced OUTSOURCED and UNSTAFFED garages in European cities.

It's no help to you, but I think Rick once wrote about a rental strategy FROM Rouen, to put your bags into the rental car and leave it in the rental garage until you have seen Rouen. (No personal experience.)

Edit: I just remembered Rick's past book comments about "Bogus Parking Wardens." We used them in Arcos and Italica/Carmona in Spain. I was dubious, but our street-parked car was undisturbed. I mainly add this so you can think in advance about whether you feel good about an old guy with an insufficient pension in a dusty Gilet Jaune. (Not making light of financial and political distress, only describing a likely possibility.)

You might have the option of packing lightly enough to fit all of your luggage under the luggage cover, but I know that can be hard to do.

What about checking out NannyBag or BagBnB or one of those apps and taking your bags out of the trunk and paying to store them somewhere near the Cathedral (and having lunch or whatever) while you are visiting it? It would cost a little money (and be a little bit of a hassle), but would give you peace of mind (and be a lot less of a hassle than getting your stuff stolen!).

I would suggest removing anything of particular value from your bags (don't bring it at all if it's highly valuable), and make sure your car has nothing visible, from outside through the windows, in the passenger compartment that might interest a thief.

When you park, pick an underground garage or an aboveground garage with a wall, and back into the spot until your rear bumper is kissing the wall, which would make it physically difficult if not impossible for anyone to try to force open your trunk -- they'll likely just move on to easier targets.

When you get out of the car, don't draw attention to the stuff in your trunk. In other words, put your purse or anything else of apparent value in the trunk before you pull into the parking garage, even if you have to double park somewhere on the side of the road with emergency flashers on some distance away from your parking garage. Don't sweat it -- it's very common and other drivers are used to encountering cars so parked. The point is, once you arrive at your garage, to make it seem to anyone observing you park that there's nothing at all in your trunk. Just get out, note the parking spot number (I take a photo of it with my phone), and leave. Conversely, a bad move, in my view, would be to get out of the car carrying a purse or something that looks valuable, and then put in the trunk once you've parked. That's practically advertising your car as a promising place for thieves to visit.

I've been driving and parking in France (including Rouen on a few trips to Normandy), Italy, Germany, and Switzerland for nearly a decade using those steps and I've never had my car molested at all. Not once.

When you pick the car up at the hire place stick your bags in the trunk of the car, make sure they are hidden. Anything you plan taking sightseeing, put in the car. After you park the car in Rouen do not go rummaging in the trunk. Make sure you lock the car.

I've never had anything stolen from either my own car or a hire car.

Have done the same in 2016 you are planning to do. I parked my car in the underground parking Saint-Marc some 10 min. walking from the cathedral in Rouen. All the luggage was in the trunk and not visible from the outside, but I had not the impression the parking was unsafe and didn’t feel unsafe too walking through the streets there. But saying this nobody can guarantee nothing will happen, but I think underground parkings are most of the time safe limiting the risk of theft.

The center of Rouen is not easy for driving around, I had to follow narrow one-way streets for getting to the parking. Certainly be aware of the TEOR fast (red-brown colored) bus lane crossing the center, is for buses only and have always right of way in both directions. The main parkings are signposted but looking around at home with google streetview really helped navigating and recognizing situations like finding that narrow road along the leftside of the TEOR bus lane to Saint-Marc. Didn’t used it but a GPS can be helpful there too.

Do all the things suggested but always carry with you your meds, computer, ID and other important documents, cameras i.e. valuables. We have a messenger bag that we load up with those things when traveling by car and carry it with us even when making a rest stop. There is ALWAYS the risk of having your trunk emptied of luggage if you sightsee with luggage in the car whether it shows or not, so at least make sure the things that would be a hardship are never left in the car.

We knew someone years ago whose entire car was stolen at a stop in Italy and another person who had all their possessions taken when stopping at a beach in France. The problem is that as a tourist you have no idea if the place you choose is the epicenter of a local theft ring that preys on tourist cars. (although if there is broken glass on the ground assume that is where you are). We have rarely stopped with luggage in car and so far so good when we have -- but we usually try to organize our touring so we have a base in an area and have the luggage stowed in the hotel and the valuables in the safe before doing our sight seeing. So we will stop for a couple of nights in a region so we can then spend a day visiting villages, abbeys etc without worrying about it.

Theft or car burglary can actually happen anywhere. Ten years ago in Anet a group of youngster hanged around my car the moment I came back from sightseeing and it was clear they had bad intentions. Luckely I arrived at the right time, they changed their mind and went away. Anet is a small town south of Vernon / Giverny a bit in the middle of nowhere, looks nice, innocent and safe but a few can prove the opposite. But I have to say this is till so far the only bad experience in this respect I ever had driving around in France for more then two decades. Nice interesting château there in Anet btw.