Sorry --- forgot the most confusing part of our process. That is, HOW DO YOU KNOW WHEN IT IS (really) LEVEL??? On our trailer, there is not a single surface that is level or square with the world. Our gold standard for level is the shower door which, when half open, is amid-ship.
After going thru the above-mentioned quarters = wood shims process, and after letting the slide out, we both ceremoniously open the shower door half way and let it go. If the door stays still, the blasted thing is level. If the door swings on it's own one way or the other, then out comes the hydraulic jack for fine-tuning in place..........unless I can convince her it is close enough.
PS. My quarters-to-tire shims chart is conspicuously mounted on the door of the trailer storage locker, and with the wheel shim thickness displayed to 3 decimal places. In reality, if I'm within 1/8" it is close enough. Engineers are taught early on that lots of decimal places creates the illusion of accuracy.
Measure it with a micrometer - mark it with a piece of chalk - and cut it off with an axe.