Running power into the bed? 2009 AC V6

All right back to running power to the solar (truck battery DC to solar/DC to be able to top it off)
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The solar is set up on the passengers side, truck battery is on the driver's side and I do not see any obvious access through the firewall for a 6ga wire.

The existing wiring harness is pretty packed. Photo below. Not sure it's prudent to pack it tighter.

I looked for other possible grommets/rubber plugs that weren't in use, (the alleged 'nipples') but I honestly don't see any.

Originally I just thought I'd drill through the passenger side of the bed and drop the wire down to the frame, But I have to cross over at some point to reach the battery.

I could bring the wire between the bed and the cab but I have no way to get in there to secure it properly. Not yanking the camper to do that.

So the other option would be bringing the power cable across the inside of the bed and coming out on the driver side,

Thoughts?

I still need access though the firewall

 

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Ride, that's almost exactly what I had envisioned for that cubby next to the power outlet. A bit over my skill level but I have a couple of questions "...it's fed by a 50A circuit breaker next to the battery and 6ga wire running to this fuse panel." Curious, what 'battery' are you referring to? The truck battery or a bed/house battery? And where did you source the lockable box? And sorry but what do you mean by 'topper's power connection.' Thank you

EDIT: and what are the 3 outlets? Thanks again.