So just as an update the cabling worked out pretty well, I just had to take my time.
I went from the above door control panel with fishing sticks, across the back of the fridge, then down the corner under the furnace. There is a run there at floor level that goes behind the toilet and behind the shower into the back bedroom. From there you can join another cable or two under the slide out, and down into the inverter bay where the slideout control module cables go. From that bay it is easy to join a couple of other cables and come out the back, and through that back firewall and out to the ladder.