I believe my Dometic manual lists how level it should be for ideal operation (it's something like 6 degrees side-to-side, 3 degrees front-to-back).
When I go to park I stick a digital level on the bottom inside freezer and shoot for less than 2 degrees either direction and I've never had a problem. Or I'll open the bathroom door 1/2 way and if it stays still on it's own, I'm good enough for the fridge.....
When I first got my RV I plugged in the power on my 15 degree sloped driveway and after 24 hours thought that the fridge was broken as it didn't get cold at all! That's when I came to this forum and learned what an absorption fridge is :)
......and I put in a level parking pad next to the garage
*Edit* I know I read somewhere about "degrees of levelness", but it wasn't the manual. Page 7 talks specifically about the topic of this thread:
https://www.dometic.com/FileOrganizer/1-international/Operation%20&%20Installation%20Manuals/Refrigerators%20-%20Caravan-Motorhomes-RV/US/RM2620%20Install%20&%20Oper.pdf