Mike,
You need and inverter that complies to UL458; that's the ABYC requirement for units on boats. It makes and removes the safety ground as it enters and exits "invert" mode.
Magnum and Outback are good US manufacturers. Mastervolt and Victron are both good products in the US Marketplace.
There are also others offering products in this space.
If all you're looking for is to power a fridge/freezer, that's a very simple and straight-forward application.
Jim
Peg and Jim Healy, living aboard Sanctuary
http://gilwellbear.wordpress.com http://gilwellbear.wordpress.com/
Monk 36 Hull #132
MMSI #367042570
AGLCA #3767
MTOA #3436
I have been using a Victron (passive) invertor on board LeeZe for the last
10 years without a hitch, knock on wood.
I have had TERRIBLE experience on my last boat that had a "active" invertor.
Lee
Levent Marina, Izmir Turkey
https://www.facebook.com/leezeforsale/