Level

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 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.

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.

Carpenters level on the kitchen island.

I use a carpenter's level on the floor, because the floor is the most convenient place to check on my motorhome. The level I have is far longer than it needs to be for the service, simply because I don't see any reason to replace a perfectly fine level. A 6" or 1' long one would be perfectly adequate.

Unless your fridge or whatever is wildly off-kilter compared to other things in the RV, it makes little difference what horizontal surface you use. They may not all be level with each other, but they won't be all that far off. If the eggs don't puddle in one corner of the frypan, and the shower drains properly, and your coffee isn't all slanty in the cup when you put it down on the counter, you're plenty level for the fridge.

My auto-levelers typically do the trick, but if out site (usually boondocks) is too far out of level and I need to do it manually, I use a torpedo level in the front cargo hold while I'm manually running the controls.

i use a small, round bubble level but after 35-years my rear end serves as a pretty good level indicator. you're close enough to level if humans are comfy and don't roll out of bed.

K Charles wrote:
If it looks level and feels level, it's level enough.

Yep. The issue with automatic levelers is that it may be level from where the level control sits. But RV frames can twist while they level, making one area level and another maybe not. I can "tell" when my rig is level and sometimes it's different than what the auto leveler says. I usually spend a minute or 2 manually tweaking it after the auto level is done. I know when it's level.

Old school (as in low technology) here. I have one of these graduated "inclinometers" attached to front TT frame (next to the LP tanks) and use leveling boards under the tires to obtain "zero bubble".

I then place a small carpenter's level on the floor and crank the trailer jack to finish the job.

I use mounted levels. But degrees off don't matter to me. I set the trailer level, mounted the one on front. Then I added leveling blocks under wheels, and marked where the ball was on 1, 2, or 3 blocks, so know how tall to build the stack.