At 300mm the moon is still only going to fill a small portion of the frame.
You'll be able to see that it's the moon, but you'll also have a lot of empty space around it and not much detail. Ideally, if you want to fill most of the frame, you want somewhere in excess of 1000mm for a crop sensor camera.
It might be worth having a look at some of the 90-100mm aperture Maksutov Cassegrain telescopes - I used to have a Meade 90mm scope with a 1000mm focal length that was also usable (with a suitable adapter and T ring) as a manual focus f11 camera lens - it worked well for moon photos, or as a long mirror lens for wildlife (though adding an improvised lens hood helped with the contrast for daytime use). Celestron's old nexstar 4 and current 4SE scopes also do well for lunar photos, and other brands like Orion and Skywatcher also do similar scopes. Also, worth checking the used market - you can often make significant savings over buying new that way.