You’re good with a direct connection to your 12v system. The X3000 accepts 9-36V. The prototype case for the X3000 actually had 9-36V DC written on it, but GL was concerned that it would confuse consumers.
See the response from GL.iNet in this thread : GL-X3000 Spitz AX input voltage range
And, FWIW, I have my X3000 connected directly to the battery in my trailer and it works just fine.