That's a nice looking job.
I guess nobody has to have a battery disconnect switch, but it sure is more convenient than pulling a fuse. And since some equipment in RV's uses battery power all the time, disconnecting the battery when the trailer is not in use is an excellent idea.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch