plastic won't stay put!

[Davo]

If the bed isn't level, you're asking for trouble regardless of the tape or goop you use to help it stick.

Normally, I'd say that if you can't level your bed to +/- .001" (one mil, or about 25 microns), lay down a raft first.

Since you are using 300 micron layers, when you slice, just set the first layer height to 250 microns - this will cause a little overfill, and the material will be forced more firmly onto the build surface. This should be enough to overcome a small variance in the build surface.