Wow, Margaret will go all goo goo over your sketches

Batteries only on the slide out. The small cables for cell monitoring are inside a second plastic sheath so no issues with small wires getting damaged etc. Normal 0 gauge battery cable will be fine for the job because it's not like it will be a continually moving process machine, just the occasional access .... well a lot more times when you first take delivery showing everyone, but it slows down after a while

The control box incorporates the battery isolation, so no need for an access way to a switch, but access to where the inverter, charger, DC to DC charger control box and tunnel heatsink will be necessary for resetting the battery isolator after the first time you forget to turn something off. Generally only happens with a 3 way fridge and it gets left on 12v after a long drive home, but the van parked under cover with the fridge and inverter still running will do it too, just takes a bit longer
I need a pathway from the area you want to mount the Dingo, Victron BMV and second Junsi to where you will mount the controlbox so I can thread the 13 core cable and data cable to run everything. Only small cables, the 13 core cable is about the diameter of a 15 amp 240vac cable to give you an idea of size.
Yes, you will need two holes in the area where the controlbox etc will live, one up high in a corner, 80mm diameter so a fan can be fitted, one down low close to the floor at the opposite corner. The fan will be controlled by the same thermostats on the tunnel heat sink, if it reaches 50*C (give or take a few degrees) the fans turn on and 5*C lower they turn off, all automatic as is every thing in the system. Alarms sound if something has been detected that was outside the control of the system and if you aren't there to hear them, the final step is to isolate the battery to save it from damage. The stuff in the fridge might suffer, but cheaper to replace than the batteries. We can even add in a two stage system shut down, one shuts off non essential loads leaving the remaining battery capacity to power the fridge and a huffer puffer machine if you have one of them that runs on 12v.
Warning, the door opening to the battery slide out needs to be bigger than the battery tray so both the slide rollers and the door locking mechanism fits. This has been one of the major time consumers on Vic's job, making the door latch functional. Missed adding the clearance the Avida type door catches require when calculating the max battery pack width and length. I sorted it but it did involve a bit of jiggery pockery type engineering
All will be revealed by the end of the week end hopefully .... yeah, no long week end for the wicked or the flogged unpaid worker of the self employed
T1 Terry