The key is it generally needs to be level when OPERATING. This is because the way they work is chemicals traveling through a series of tubes by way of heat and gravity. If not level, the stuff can't travel through the tubes properly. If it happens long enough, the cooling unit gets ruined. When you get your BT, look at the stickers on your appliances and download the manual. The manual will tell all. Generally, the allowed slope is 3 degrees left-right and 6 degrees front-back. I've also heard that if walking in the RV and it FEELS unlevel, it probably is too unlevel for the fridge to work properly.
When traveling, since the angles are often changing and not stationary for an extended period of time, it is acceptable to run the fridge while in motion or driving. Depending on how long your drive is, you may not even need or want to keep the fridge running, as a lot of people don't like to leave the propane on while driving. It just depends on how long you'll be travelling, how full is the fridge, how hot is it outside.
The fridge thermometers you can buy are neat. You can set an alarm to go off if it gets too warm or too cold inside. Since you need to get in the habit of turning off the fridge and any other propane appliance before pulling up to a fuel pump, sometime I forget to turn it back on in my hast to get back on the road. More than once the alarm reminded me.
Here's a video with the short answer...
https://youtu.be/LdtHFD8i3PA?si=IdeNiImwzV4CuFkQ
A short video with visual aid...
https://youtu.be/cy1W-uWvR9U?si=9xjurRPZ0H7S7lkz
A longer, in depth video...
https://youtu.be/9B7XTk0FyCU?si=jWCUgqi2IinJNSe8