I am going to install an inverter this summer so I can run the frig without the generator. Does anyone have any recommendations on newer inverters and maybe a wiring diagram? How do I run the 120 into the main panel?
Your question is not a simple one to answer in that there is a lot of electrical system data that needs to be determined. You need to take a total systems approach to your electrical system to get you something that will work well for your needs.
To install an inverter correctly, you need to take an energy survey of the appliances and systems that you want to power from the inverter. You then need to consider how many hours you want to power this load from the battery bank and at what percentage of total load you can get by with proper energy management.
This will give you a number to determine the capacity of the battery bank. You will also need to consider the time required and the source of the power to recharge the inverter battery bank. The type of battery chemistry will also effect optimal discharge depth and recharge rate.
There are cheap junk inverters, cheap low feature inverters, and good quality inverters. You really should choose a full sine wave inverter. Many devices will not like the waveform of a none full sine wave inverter and either run poorly or maybe not at all.
If you choose something like the Victron Multplus inverter, it already is designed for easy integration between shore power, the generator, and the inverter powered line devices. This inverter also has a built in battery bank charger of adequate size. the 3000W 24V versions are popular. I would also recommend to use a 24V battery bank. This will cut the current requirement in half of a 12V battery bank, save wire costs, and in general increase battery longevity.
I have included a pdf from the Victron site that is a good starting point for any good inverter system design. You don't need all of the bells and whistles but it is an excellent example of what a well designed system will look like.
If the only need for the inverter is the fridge, perhaps a fridge that runs on both 12 volt and 110 would be cheaper than the inverter and associated installation costs.
How big of a fridge is it? Is this a home unit or a marine model? If marine, perhaps it already has the 12 volt side.
The Norcold fridge on our 47 runs on 12 volt underway and 110 volt at the dock.