i always recommend against doing this
because it was not designed for that purpose
it is there so you don't have to switch something manually before applying power
Not to switch between HOT circuit power choices
transfer switches on EMG generators and equipment
activate when utility POWER is lost, and are much heavier rated and tested on a monthly basis ( i used to work at a major airport )
not willy nilly switched during working loaded conditions
a pitted sticky contact, cause by arcing when switching loads, could ruin your whole day, or cause sever electrical damage to the RV
yes minimal loads such as battery maintenance charge should not cause problems
but why risk problems that can be avoided
bad habit to risk getting into
once its a habit, you do it with the A/C and hot water on, with out stopping to think about, do that a few times and the contacts in the switch will be collecting arc marks and pitting