I think that parking on most any slope with in reason as long as the fridge ect is off will not damage any thing on the rig. As long as you can get around in the rig. However if the Fridge is on you need to at least follow the general we have followed for 40+ years. If you are comfortable in the rig and a beer or soft drink can does not fall off the table you are good. I know many people will say you need to be exact level and some use a lazer to level even in rest stops. However in all those years and over a million miles of travels we have never had any problem with a fridge in any of our rigs.
We do have small bubble levels in the rig and when we stop at rest areas ect. my wife will read them as we pull in and many times just by moving forward, back or left or right you can make them better. We always travel with our fridge on unlike some.