Does it matter when/if you turn on the battery disconnect.
Well. I will give you two scenaros
One: Plugging in at an RV park
1: Turn OFF park breaker
2: Plug in
3: Turn breaker back on
In this scenario you may leave the battery connected or not your choice. IT should be turned on when connected so the battery can charge in most cases (There are exceptions but none of them have been made this century). If you already had the battery connected on the road (As I do) no need to disconnect.
NOTE: when you unplug. Start by turning OFF the park breaker.
Scenaro 2 Plugging in at homem LIVE outlet
It MIGHT make a difference. in which case you need to minimize load. but a better option would be to turn off the MAIN breakers in the RV before plugging in and again before unplugging Then turn them on once plugged in again.