A "50A system" can draw as much as 12,000 watts (12 kw), so that's a major size genset and not really portable. However, in practice you can probably run most of what you need (2 x a/c units, fridge, water heater, and some miscellaneous) on about 6-7 kw. The biggest problem is that the a/c units have a high initial demand to start the compressor, so you need a good sized genset to handle that.
So, look for a genset that has a PEAK load rating of at least 6 kw, with 7 or 7.5 preferred. This is not going to be a genset you can pop in and out of a storage area or the back of the truck, so figure on a semi-permanent mount somewhere. Weight will be 175-200 lbs, and you may want electric starting and a fixed fuel tank to feed it.
Some people buy TWO 3 kw gensets that can be operated in parallel. That makes them easier to move around (individually) and some of the time you will only need to use one, e.g. no a/c needed.