Best Of

We recently ran a large SOOW cable from a gen/shore transfer relay located in the driver's side wheel well area to a generator (*) located on the tongue/A-frame area of our '23 320.  This same run should work well for your proposed run of 4 gauge cable for your dc2dc charger install.  Here's how we ran it:

1) Removed the black, plastic shroud/box located on the exterior, just underneath the shower drain.  For steps 2 and 3 it might help to fish a smaller wire through first, then pull the cable through.  2) From inside, ran the cable down the front side of the wheel well through the opening near the floor leading underneath the shower pan.  3) Pushed (or pulled as the case may be) the cable forward, alongside the shower drain plumbing about 12-18 in. then down through the opening in the floor (previously covered by the black box). 4) Cut a hole in the black, plastic shroud/box to route the cable through.  5) Reinstalled the black plastic box.  6) Secured the remaining cable with cable clamps as it traversed its way along the frame to the tongue/A-frame area. 

This being said, there may be other options to consider.  Lots of collective knowledge here.  No doubt others will chime in with more mounting locations and cable routing options.

We've installed a number of dc2dc chargers in previous RV's and tow vehicles we've owned.  Here's a few tips we learned along the way:

Have you decided on a 12v ignition source to activate the dc2dc charger (D+ terminal on a Renogy)?  Many folks run a wire from the ignition or other switched 12vdc source to the dc2dc charger.  That's a bit of work and still leaves you vulnerable to discharging your tow vehicle battery if you inadvertently leave the ignition (or switch) on without the engine running.  You might consider installing a generic battery isolator next to the dc2dc charger instead.  The battery isolator will only activate the dc2dc charger if the voltage on the dc2dc charger's primary input is greater than 13.3v. The alternator must be online producing current in order for this voltage to rise above 13.3v; otherwise, the dc2dc charger remains off.

Also, most vehicles have battery/alternator to frame/negative connections that are capable supporting the full rated output of the alternator.  This allows use of the vehicle's frame for most of the negative cable run---saving time and money.  Instead of running a negative cable the entire length of the vehicle (battery to rear bumper), simply make a secure negative connection to a primary frame member somewhere near the rear bumper of the vehicle. From there run the negative (and positive) cables the remaining distance to the 320. Recommend using a 175a Anderson connector (or something similar) as a disconnect point between the Tacoma & 320.

Hope this helps, @VonAustria.  Good luck with your install!

(*) We chose to use a Honda 2200 generator we had installed in the tongue/A-frame area (secured inside an enclosure) to perform charging duties while driving (vs. a dc2dc charger) and to provide full generator support while camping. Due to the high efficiency of the Victron Multiplus II 3000 charger we use, we're able to net 90-95a of charge current while only drawing ~13.5a from the Honda (prefer to run the Honda 2200 below its 15a continuous current rating).