The real question is what are the total power requirements and how long will you operate with DC battery power running the fridge, lights, pumps, etc., and the inverter powering a freezer and misc ac loads, you may find that the amp hours available from 2 8D batteries may not be sufficient for more than an overnight (if even that).
Don't even consider connecting the water heater to the inverter (or the air conditioner). The power draw will be too high. You should be able to maintain hot water by running the main engine if you have a coolant loop installed.
Many websites that sell top quality inverters (Magnum, Victron, Mastervolt, Outback) have information on how to determine your power requirements in order to properly size your battery bank and inverter.
As the other posters have recommended, fixing the generator may be a better solution. Adding a quality inverter, battery cabling, additional batteries, AC wiring, adds up in cost rapidly. Adding one of the new quiet Honda generators is also an option. I would be paranoid about CO poisoning and be careful about where it is mounted. It makes me cringe when I see sailboats anchored near me with one of those generators mounted on the cabin top and running.
Good luck, I'm curious as to which way you decide to proceed.