I'm a newbie here but you might be interested in my general experiences from doing this for a few years.
The places I have had good success with have been fairly small places on the edge of town with lots of passing trade but the important things are hard floors and gaps under the doors. That said, I recently got an amazing couple of catches from a place with rubber insulation seals around the doors. I thought it would be a wash but went out anyway and the quality I got was amazing.
Avoid the big budget-hotel chains (Etap, EasyHotel etc.) as most of these do seem to have CCTV in the corridors. Slightly more upmarket chains don't (Ibis, Comfort Hotels, etc.) so I'm guessing that cams in the public areas - even discreet ones - make a place look unwelcoming to people who are happy to pay a little extra (not surprisingly!).
The other thing to watch for is that the hotel shouldn't be too full when you visit. Couples tend to be a lot more inhibited if they think someone is in the next room. So avoid peak times.
One last thing… Go pretty much anywhere in France. The French are totally uninhibited in bed and nearly all my best catches are from French-speaking couples. Which reminds me. Must get round to sharing them…
