we need more info to help you.
you can tell us what type of rv you have in your ''signature block''.
how many and what type of batteries do you have?
how many amps or watts does your wally world fridge consume? is it operated by a freon compressor or some other way?
many motors (freon pump) will not run at full speed and will overheat if operated off of a modified sine wave inverter.
full sine wave inverters are expensive while modified sine wave inverters are cheap.
my 750w modified sine wave inverter operates my entertainment systems (2 crt tv's, vcr-dvd recorder, and 2 digital converter boxes) just fine for several hours.
(300w/12v=25 amps, times 6 hours = 150 amp hours.) my previous 300w and 400w msw inverters were marginal.
my house battery bank consists of 2 300ah lifeline agm 6v batteries wired in series. you do not want to discharge deep cycle batteries more than 50% regularly if you want them to last.
lifelines are expensive.
here are some resources for you to check:
The 12volt Side of Life (Part 1)
Amps and Wire Gauge - 12V Circuit
RV Tech Library - True Sine Wave versus Modified Sine Wave
Lifeline GPL-6CT Battery