I think if I was to do this job I would just Run a new fused feed from the battery up the passenger side fire wall and install a separate set of outlets using the proper sized wire for the load you anticipate having + a safety factor so you don't burn you investment down. Plus you won't have to drill your dash or remove radios or take a chance of cutting into wiring or any of the head aches that all this can cause down the road ie loose wires bad connections and the like. you can get mounting brackets and such to put it under the edge of DW side and both of you will be happy campers
