Here are a couple more on simple battery switch installs... Should not be hard to install yourself...
I have seen several installs using that type of battery disconnect switch. Most of them is mounted in the lid of the battery box but if I was too do that I think I would want it on the bottom part of the battery box like shown here. I guess you have more mounting room if they are mounted in the removable lid but the you have to deal with longer cables so you can remove the lid for battery maintenance.
I see some of those switches have a key handle that is removable and then you can cover the keyhole with a plastic/rubber cover.
I saw one dude used one of those twist disconnect switch and had it in series with his auto-reset circuit breaker. Looks something like this photo. I thought that was a pretty neat way to disconnect power like to your POPUP raise roof up/down switch or trailer landing gear. It always bothered me having those switches mounted on the outside of trailers where kids might want to play with them to see what happens...
sample photos from google images - not mine