Reddit reviews Blue Sea Systems m-Series Mini On-Off Battery Switch with Knob- Red, 2-7/8" x 2-7/8" (6006)

Any competent electrician will warn you against repeatedly using a breaker as a switch (but yes, I have). They DO have a limited lifespan. It's big, but so are the consequences of you being unlucky and it failing. I'd use a dedicated switch (I use this: https://www.amazon.com/gp/product/B00445KFZ2/) and a fuse rated to 150% of the max expected current. Keep in mind, your inverter is designed to handle a surge, and most electrical things draw a huge surge when they start for a brief moment. You have to consider that current in your fuse selection as well. I always kill the inverter when not in use. It arguably increases its lifespan as well. It's one less thing to fail while I sleep, while I am away from the van, or while I am driving down a mountain in snow!!!

I bought a deep cycle battery and connected it to the car starting battery with a switch http://www.amazon.com/gp/product/B00445KFZ2/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1.

You turn the switch on when driving, which allows your deep cycle to charge, and turn it off when parked so it doesn't draw from your starter.

I then wired up a cigarette lighter to my deep cycle and use it for a 12 v fan, phone charger, and 12 v laptop charger.
http://www.amazon.com/gp/product/B001JT7B3A/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

You drill a hole in the floor of your van and run at least 4 gauge wire from the positive pole of your car starting batter, to the positive pole of your deep cycle with the switch in line. Then you ground your negative pole on your deep cycle to the frame.

After that you can add on whatever components to the deep cycle to draw charge with ring connectors.

The draw back of this set up is that you MUST turn your switch to off when parked otherwise you can draw power of your car battery and be unable to start your car.

I like Blue Sea switches. Used them on boats for years. Whatever you get, make sure it's rated for the amps you pass through it.

The fuse/CB size should be the lowest for whatever the max the circuit will draw and the wire will support. Say a fridge draws 4a at normal running but 12a starting, then the fuse should be 15a and the wire sized to the 15a.

I fused my 2 series panels at 15a since 10a would not be enough, so I have 2 fuses because of series 2 in parallel, both on positive side of the panels. You don't need to fuse both sides.

I fuse and switch positive.

Battery cutoff should be before the first load off the batteries and completely isolate them.

The victron BMV will work by itself, all it needs is the shunt and a positive lead.

I disagree that is the "best" MPPT, but use what you want. That one is cheap, but their support is direct from china and they have more than a few reviews of people having hard times with warranty and support, that plus it is very large.

I like Will's videos, but my experience with the victron is not anywhere like what he complained about. The connections are solid and it doesn't get hot at all. Initially I was concerned, so I put a temp monitor inside the compartment and a 12v computer fan on the vent, but even without the fan the compartment that is about 2' x 1' x 1' and under a couch is only about 2 degrees F warmer than the rest of the van when in direct sunlight pulling in nearly all of the 400W.

Fusing the 200a draw is not about the amp-hours of the battery. amp-hours are how long it can discharge, not how fast. you need to find out what the max discharge rate for the batteries are, and the max amp rating of the inverter and size your wires and fuse according to that (along with the length of the run)

"going up one size" on the wire is a general term. Use this instead https://www.wirebarn.com/Wire-Calculator-_ep_41.html