In the middle of this right now on my truck, although I am not running power up to my roof rack. Running power from 2nd battery to BS fuse panel in the back. From there running x5 power ports, camp lights, fridge and probably a compressor. Gutted the interior, had to buy some new clips from Toyota for the panels. I needed to replace the RHS cargo window motor so doing it all at the same time. Cleaned all the panels up while out, washed carpet ect ect. I really dislike these type of jobs but in the end I will be stoked. I have not ran my big power wire yet through the firewall but have ran a few others already, LED light bar switch and 2nd battery monitor. Don't know if I will drill through the firewall, probably not, just punch it through the stock grommet and go, silicone if I feel the need. On my 80 I had both batteries in the back, had a butt load of big wire running to the engine bay, I ran it all under the truck. It work, it was ok but I would rather it is inside the truck so that is how I am doing it this time.
Cheers