I had been running my inverter thru the distribution panel for many years by plugging the shore power cord into a 30 amp receptacle that was hardwired to a Xantrex 1800 inverter. If you are familiar with electrical circuits and you take some precautions, this is an inexpensive and easy way to power your entire rv. You must of course first turn off the converter circuit breaker, and any other device that will not operate within the capacity of the inverter and/or batteries, such as the air conditioner, water heater, etc. This setup worked/works very well, but I wanted to avoid flipping circuit breakers and having to go outside to fumble around with the shore power cord when setting up camp for boondocking. I could have gone the traditional route and installed an automatic transfer switch and a subpanel, but these switches must stay energized all the time when in one position or the other. Additionally these switches are not known for their reliability.
My answer was to install a manual transfer switch which does not use any power in any mode, and is highly reliable. I have seen this done with standard double pole/double throw(dpdt) toggle switches, but these switches are not designed for this purpose and should be avoided. As it turned out I already had the perfect switch in my companies inventory for the industrial service work we do. A 6 pole/double throw, 600 volt, 32 amp, rotary switch for switching between two power sources, and an off position to boot! This is very similiar to switches installed in marine applications for this very purpose, but absent in rv applications for some reason. Although marine manual transfer switches are very expensive, they typically only have 2 poles. After using 2 poles for the hot and neutral connections supplying the panel, I had 4 remaining poles to disconnect power to the other items when in inverter mode. This means when in the shore power mode, power is passed thru the switch therefore supplying power to the panel and all of the circuits. However when in the inverter mode, power is still supplied to the panel, but power is interrupted after the circuit breakers to the selected circuits with the remaining 4 poles of the switch. I my case the refrigerator, air conditioner, water heater and converter. It is important to note, to avoid any type of inductance or capacitance issues between power sources, I always "pause" in the off position when switching between modes. Also, the Xantrex 1800 does have a built in automatic transfer switch, but the pass thru is limited to 20 amps if I remember correctly, so this was not an option.
You can configure your own switch here. https://www.c3controls.com/cam-switch-changeover.cfm
If you do not require 6 poles, the switch can be configured with less poles. Cost is the same or less than ATS as a subpanel and alot of additional wiring is not necessary. This modification makes use of the existing panel and breakers! The only wiring added was to the refrigerator and converter. I had approx. 4' of existing wire coiled behind my panel that made splicing into the other circuits very easy.
I had planned on making a cover or otherwise trimming out the box but it is still on my to do list.