SamB
Shut up and play!
Re: The Orsha Plain
A: Yes, as per the ASLRB there is nothing to preclude you from doing this, though you'd be better off not doing it since you can save the trench for another/better location. Per B27.6 you could move directly from the gully to the trench without coming out of the gully first and then entering the trench.
The problem with using the gullies is that a gully is open ground for OBA and attacks by aircraft. My current opponent has placed several fox hole in gullies. (A trench would be better in that you can move into / out without exposing yourself outside the foxhole)