1. Decide what you want to run from inverter.
A. Is it hard wired or is there a plug?
B. If it is hard wired, do you want to leave it that way and in or out of the inverter supply?
2. Do you want to select and de-select the inverter or always have in the circuit?
Many years ago I installed a Freedom 1000 inverter/charger in my cabin cruiser so I did not need to run the genny to keep my beer cold in the fridge. The fridge only uses about 100 watts when on, probably 40% of the time at most so I included one light circuit and a duplex outlet. The fridge is hardwired as is the duplex outlet, the lights are also but they are switched. When I did this installation I did not have many battery powered tools, mainly lights etc. so having a dedicated 120VAC outlet with 1000 watts available was pretty neat, my big plug in inverter was all of 150 watts and was leading edge.
My thoughts: If you use a 115VAC fridge put that on the inverter with selector switch to allow line or inverter. Microwave, never, they are seldom happy with inverters unless there is a major surplus of capacity. Lights, go led and no need for >12vdc. Heat, you have 12vdc fan and controls for gas, likewise HW. If you decide you can't live without TV get an LED that has a 120VAC to 12VDC converter and rewire the input to either a cigar lighter connection or hardwired 12vdc. Also, when installing a radio, get an HD radio, I prefer the Kenwood KDC-HD552U. HD let's you find more options on the dial without needing to subscribe to pay radio.
Keep us informed, updates with photo is better.
If you want to put the inverter in-line then consider a marine, make before break selector switch. http://www.perko.com/catalog/categor...s/product/148/
If you feed it backwards then the supply is selected to the load. I use two and have two battery banks. It requires a drawing at my age but it is reasonably straight forward, minus martinis.
Better thougths, straighter thoughts tomorrow.