All CGs I've visited have a quiet time (starting at 10 or 11pm) and don't allow generators at night no matter how quiet but there are some places that don't care as much. I think this is because if someone runs their very quiet unit, anyone would complain, "How come they get to run theirs and we don't?".
Most dual portables only get you about 30 amps. 2 EU3000s provide 50 amps but I don't think they would fit in the front compartment.
If you plan to use a generator only for RV power then I would think it's easier and more secure to permanently mount an Onan compared to portable units. They also tend to have larger fuel tanks which mean they run longer. At night unless you are camped in the Arizona desert in summer, you should be able to get away with not running the gennys and rely on 12 volt battery power each night for the furnace, water heater, and fridge. You can have an inverter installed for the televisions and other 110v electronics (not sure about Air Conditioner).
I use twin portable EU2000 Hondas with a parallel cable to get 30 amps of power. If I feel a need I can buy a third EU2000 and use this:
http://wisesales.com/ (scan towards the bottom of the web page and look for a "triple cable") and support 50 amps of power (actually about 45). However, I think an Onan 5500 would be easier to fire up when you need it. One advantage of multiple gennys is if one fails, you still have a backup (less power available, but....)
Hopefully a search of this forum will find some members who have done these to help you with your decision, especially about installation. I notice camper4 has an Onan 5500!
Way cool!