Slitherine

I can't see anywhere in the rules that prescribes what "formation" artillery can be in if unlimbered. So can I be 1 wide and 2 or 3 deep to squeeze into a gap? And if so is it a formation change to go from 2 wide to 2 deep?

you can form them up in a column and run down a road or follow said road through an area of buildings or even over a bridge. Once the deploy then I think you would want them in a single line though

I think going from 2 wide is forming a march column and is covered on page 39 last bullet right column, no CMT is mentioned so you should be able to do it. You just move from tactical to a single line as a march column and off you go. Likewise you start in a single line march column and can move the arty to a 2 wide tactical formation no CMT required.

I can't see anywhere in the rules that prescribes what "formation" artillery can be in if unlimbered. So can I be 1 wide and 2 or 3 deep to squeeze into a gap? And if so is it a formation change to go from 2 wide to 2 deep?

We've never really found anyone wanting to unlimber 1 base wide.
Basically it isn't an allowed formation - so you can't do it.

If anyone realy realy wanted to do it, I should point out that units in column can't fire.