Electrical setup sanity check

" - If I did run the car with the panels plugged in (input from both DC/DC charger and from panels) would this be a problem?"
No problem at all.
Cheers,
Peter
OKA196 motorhome

To my understanding, the dotted red line is wrong. I understand the intention, but an unregulated panel should not be connected directly to a battery. It should go via the MPPT regulator.
(I may be wrong here!)

Redarc sell a battery isolator that monitors the starter battery and if the voltage drops to a set level it switches over and lets the solar top the battery up so you don't have to monitor it yourself. I set one up yrs ago when the aux battery was connected to the starter battery via the Redarc isolator and solar was attached to the aux battery via it's own solar regulator. Simple setup that works well.

Dont forget you will also have to alter the output when using the MPPT solar regulator to lithium for aux battery and lead acid for start battery.

I just mounted 2 MPPT solar regs in the car and switch the solar panel cable to appropriate anderson plug for either the start or aux lithium battery.

Final update for anyone stumbling across this (I hate when I find a partial thread). The setup in the above threads has worked a treat, thanks for the help guys. Summary..

See threads for actual solution, initial diagram is not right.

Triton MR Dual Cab.

50amp wiring from crank battery under the hood with 30amp fuse right up close to the battery. Ran it through the chassis frame mostly, was careful to make sure it wasn't gonna rub too much anywhere.

Brought it up into the cab where the taillight loom went in. Was about 5 meters, was no voltage drop that my multimeter detected.

Straight into a "Ridge Ryder 140A" isolator. Then out the other side into a single anderson plug. This isolator will let your aux battery charge when the voltage is high enough (car is running), and not let it drain your main battery to start the car. Then into..

Engel battery box series 2 via DC/DC charger, same as plugging it into ciggie plug. This is a great piece of gear and you can get the mount so you can slide it out and carry it to camp if you cant park close (side note, 120AH lifepo is almost exactly 1/2 the weight as an AGM battery of same capacity). Has 240v 300w inverter, USB. BUT, and this is annoying.. It wont charge unless you have the screen turned on. So you have to leave it "on" for the car to charge it but leaving it on means the screen draws a bit of power. It's fine mostly, but if your car sits there a few weeks then your aux battery is gonna discharge for no good reason.

DC/DC charge on the Engel box is fine for me but it's not quick. It puts about 60W in, this means a lot of driving to charge a half full battery (like 9 hours). 200W solar blanket puts about 130W in. My draw is just fridge (40w max) and some lights at night and a few bits and pieces like torches and things. So I reckon it will do just fine unless there is no sun for days.

Also, when mounting stuff into tray, dont be an idiot like me and make sure you drill the right size hole so you dont snap your SS screws off.