Vent a Tank Cabinet with a Sump?

I didn't, but the back of the stand is open so any excess heat or humidity would escape.

Agreed, as long as the back is open, no reason to add other vents.

The back of the stand is exposed so it is all oak. I could vent at the top where the lid attaches to the stand.......

I water proofed the entire insides, it's pretty tight. If I ever did get a leak water would fill until coming out the cabinet doors.

I'll look into venting. how big a vent or holes do I need?

Thanks