This measuring jig fits between the top of the z-motor mounting plate and the bottom of the x mounts. When it fits about the same on both sides you should be good to go! -Alternatively you could make two of these and lower your z until it bottoms out on both.

My printer as it is setup up currently rarely needs any adjustment if the bed is well leveled once. I just do a quick 4 second check with the jig after homing and about 10% of the time I may need to turn a z motor a click or two. Good enough for me!

I feel I should note that one simple thing that I changed on my Tronxy P802E that made a BIG BIG improvement on getting a consistent bed level was to replace the horrible acrylic bed undercarriage with a solid aluminum one. https://www.thingiverse.com/thing:2545713