Level

Carpenters level on the kitchen island.

I spend 2-3 hours obsessing over it

Friends wife took a trip without him. Her camp spot was pointed downhill. She pulled in forward, put the leveling ramps under the rear tires and was happy. I offered to help, she declined. Don't no matter to me.
Worst part is that now I have that camper's fridge in my garage. Somehow it still works.

I have a pair of those little Eagle stick on levels, one on the road side front corner and the second just around the corner on the front. I just use them to verify that my auto level zero point hasn't changed.

A 2' level on the floor by the door works for front to back.
A 2' level on the exterior wall works for side to side.

I just use a simple $6 bullseye level

I try to get within half a bubble of level which is enough that the RV doesn't "feel" unlevel. I do have an absorption fridge so need to stay within a few degrees of level, but the real limiting factor is that water pools in the corner of the shower and/or kitchen sink if the RV is too far from level. (and it's opposite directions, the shower doesn't drain if the RV is tipped too far in one direction, the sink won't drain if the other direction)

I do a spot check on the dining table, then follow up with a check on the floor just case something knocked the dining room table off level.

I use a simple round bubble level placed on the floor between and behind the front seats. Easy to see from drivers seat.

Try the dollar store for the cheapest level you can find.

3 degrees is 5" drop across a 8' wide RV, good for the refer and not so good for humans. For every 12" on the level 3 degrees is 0.6".

I use a T Level,place it on the floor of the freezer compartment,works for me.

And LP fridge will need to be 3 degrees or less level. 3 degrees is a lot of off-level which you will not be satisfied with, so for the fridge, if you feel it is level then the fridge is likely very happy. For you, if you are happy then it is level enough. I would suggest to get used to living every so slightly off-level if you camp a lot, this makes life easier. As long as the eggs dont run too far to one side of the frying pan you are level.

I have a pair of levels calibrated in inches with one attached to the dash and the other to the driver's side panel. They let me know quickly if I'll need any supplemental blocking under my automatic jacks and how much. I leveled manually using a carpenters level before attaching them.

RV Designer E401, Stick-On Level, 2 Per Pack