This most likely does not apply to 2018's and later, in my 2017 VTDP I have an AV compartment over the driver's seat. In this compartment there is no 12V wiring that I could find nor know what it's connected to should I need to chase down a fuse. I wanted a 12V run into this compartment to connect my Pepwave units (2) to 12V and not have 120V plugs to deal with as one recently fell out without my knowing as the redundancy I have setup kept things online. It's probably more efficient as well for boondocking and also give me the ability to take the inverter offline and keep Internet online.
I originally thought I would just take the A pillar black plastic cover off and find a red and white, verify voltage and splice into it. That would work but as stated above who did I just cut power to and what fuse does this line belong to? Then I came up with a better plan. I have 2 x 12V receptacles left of my steering wheel that I know what fuse that's connected to, I'll just tap into that.
It's actually quite easy to do which is the gift I'm going to give you
1) Remove the driver's side window MCD shade
2) Remove the A pillar plastic cover
Now you can push a line out the back left of your AV compartment, no fishing wire needed, see it near the driver's side window (shape it to flow left) and then just pull it on down. You can run the wire to under the dash with ease and make your connections. It's that simple.
The pepwaves are very easy to wire and require a 2A inline fuse.