12VDC battery heaters
I recently installed a solar system and tank heaters on a Kodiak Cub, and here is what I found.
1) It did not have a 120VAC inverter from the factory, and the owner did not want one. So we installed 12VDC tank heaters (Ultraheat) instead of the usual 120VAC heaters. This has the small advantage that the heaters will still work while you are driving and not connected to shore power. The heaters have a total draw of about 13A. Since the truck 7-way plug only supplies <10A (usually more like 5-8) they draw down the trailer battery by 3-5A while driving.
2) To counteract this, we used two 100AH Lithium batteries on the tongue. This gives him lots of 12V power with VERY light weight (<60#). These lithium batteries will last 10 years or more.
3) The dump valves are NOT tucked up under the belly insulation. So we had to add Ultraheat pipe and valve heaters. They draw another 8A from the batteries. It was not simple to build a usable box around them, but we eventually figured it out. The dual lithium batteries are now more needed than ever!
4) Since the tank heaters use a combined 21A DC, we found an unused 30A DC circuit in the panel and wired them to that using 10AWG wire. It is my understanding that some Cubs don't have an extra 12V DC circuit in the panel, so you could wire it directly to the 12V lines into the panel using an inline 30A fuse. DO NOT EVER WIRE ANYTHING TO 12V WITHOUT THE APPROPRIATE FUSE. It was not difficult to route the wire to a switch a few feet above the breaker panel. We simply used a 30A rated Automotive toggle switch (lighted) . Routing the wire back down to the tank heaters required drilling a hole in the floor behind the WFCO panel, then sealing it.
5) The standard WFCO 8700 power converter in this Cub was 35A, not enough for all the 12VDC heaters, so we upgraded it to a 45A Power Dynamics converter. The biggest converter from WFCO for this panel was 40A, which is why we went with the Power Dynamics. For a few bucks more, we could have gone with the 65A converter, but decided it was not needed.
6) Since he is often cold weather camping, we also added 12V battery heaters with a switch. They draw 4A. We connected these directly to the batteries with a 15A fuse. We wrapped the battery box in Reflectix and glued and stitched it on for extra insulation. Batteries really work better when slightly warmed. Lithium likes to be between 40-60F, lead acid likes between 50-80F. Below 32F, he simply flips the switch to keep the batteries warm. He must remember to turn it off when above 40F.
7) All this 12V DC draw is somewhat mitigated by two 170W solar panels, one on the roof and one portable that can be set 50' away for when he parks in the shade. We use a Victron MPPT solar charge controller.
Hope this is helpful.