Best way to power the transceiver is to run a separate set of heavy wires direct to the battery bus bars where the battery cables connect. Fuse the hot side there. For 20 amps, you need a minimum of #12 wire--the ones you have there don't look big enough.
In our AS, we have an FT-857 setup. The head is remote cabled to the desk in the rear of the cabin, and the main unit is mounted in the streetside wardrobe cabinet. The main unit is powered from a PowerWerks distribution panel mounted near it. The line from the battery bus bars under the front bed is a dedicated #12 red/black zip wire that ends in a 40 amp powerpole connector plugged into the distribution panel input. Makes it easy to shut it down when in storage. Antenna leads are also available that connect to feed-throughs that go into the refrigerator upper door area from the wardrobe. We can connect portable antennas there. A UHF/VHF whip is also run in through the solar panel combiner box that accesses the top of the wardrobe.
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.