These are the in-line crmip fuse blocks I found.
The next step (after the new potting compound arrives) is to find a suitable location for the switch in the car, make the wiring harness and install it.
Like this:
When I searched around, there is a commercially made version of what I am building, but I could not find one to switch 3 circuits; only 1 or 2.
And the cost of the commercial version was over $100. I figure with the molding and potting compound (which I can also use for other projects), I have slightly under $100 invested in my version.
Again, my version can switch 3 circuits, and at 25A, where the commercial ones can only switch maybe 10A at the most as they use a fairly cheap switch. You can also see the commercial version just has terminal lugs on the ends of the wire - not the nice connectors I molded.
So I started this project out of necessity of switching 3 circuits, but ended up making something better than the commercial version.