Use your level, not the mount bubble level. Having said that, it's really the least important part of getting good performance from your mount. All that the leveling accomplishes in a GEM is to (other than keeping it from falling over) is to make the initial star alignment process easier. Once you've polar aligned the mount and performed the star alignment process it has no effect on goto's or even on guiding performance.
Ross is absolutely right. A reasonable leveling will ensure the first go-to star will fall into your field of view with minimum effort to center it.
Oh, you might want to switch the pin on your tripod, the polar scope is much easier to get to when the pin is over the front facing leg. I don't know why iOptron ships the tripods that way to begin with?
It's more important to establish a reference level point, rather than an absolute level (unless you're on a stationary pier). Then square the RA and DEC axes to the reference level point, and you can easily setup night after night.
Cheers and good luck with the Z...