If it s my choice i ll mount a panel directly to a concrete or block wall.
Mounting a sub panel to a concrete basement wall.
Only 1 8 or so but it keeps the moisture out.
This just makes sense because you connecting the sub panel directly into the existing panel.
As stated above most if not all panels have dimples in the back of the can to provide a bit of space from the wall.
Then remove the tape.
Just a drill and a piece of wood will.
Normal placement of your new sub panel will be down in the basement directly beside the existing electric panel.
Basement is always dry no sump pumps no moisture coming through foundation wall.
I usually use tapcons.
Tape a one foot by one foot square of plastic sheeting plastic kitchen wrap will do to the concrete wall in your basement with duct tape and leave it in place for 24 hours.
Since the sub panel is only 14 wide i will still have at least 3 of space between it and the main panel as well as between it and the adjacent wall.
And the shorter distance between the two panel means a cheaper installation.
As an alternative i could always mount the sub panel on the adjacent wall so that it s facing 90 degrees to the main panel.
Very low water table area.