Many generators are really noisy, and therefore annoying to any other
campers in the area.  Generators rated at or under about 60 dB are very
neighbor friendly.  Louder ones are not.  There is no easy way to make most
generators less noisy than the way they are when you buy them..  Changing
mufflers changes the engine dynamics and may decrease engine output and
change engine life.

Generators come in several flavors.  Some are made for continuous use (for a
few days or weeks) and others are really only designed as emergency back-up
units to run for a few hours at a time.

Generally it IS as simple as adding up the ampere rating all of the lights
and appliances you will be maximally be using at one time - then adding a
buffer factor, perhaps 20%.  Generators are usually rated at continuous and
peak outputs, peak meaning that they can kick-in a little extra power for a
short time when, for example, starting up a motor.  Unfortunately, most
generators advertise what their peak output is, and what you really want to
know is what their continuous output is.
The size of the fuel tank, and therefore how long the generator can run
before filling up the tank, is also important.

Running the AC off a generator is the biggest load, and may really increase
the size you would need.

One does not need to spend $1800 to have a relatively quiet generator.  See
the article at:
http://www.campinglife.com/site_page_905/article_page_250.cfm
reviewing 3 quiet relatively light portable generators.

Here is page illustrating what dB noise levels equate to in the real world:
http://www.generatorjoe.net/page.asp?id=52
and, from the same site, some db ratings of some generators:
http://www.generatorjoe.net/page.asp?id=53

Yours.

If you can get away without running the AC, you can probably avoid buying a
generator.  Your fridge should run off of propane, as will most everything
else in the camper (except the microwave).  You can get an inverter that
would run your microwave and most other 110v devices off of battery power.
Those electric coolers will suck a battery dry very quickly.  I did some
digging into options other than a new gas/electric fridge when I was looking
for something to put in our camper...those thermoelectric coolers aren't the
answer.  If you need more battery capacity to run the gadgets and gizmos,
you can always add a 2nd battery to the system.  Then another option would
be a smaller generator to use for short periods of time to recharge the
batteries.  Also keep in mind that some campgrounds may limit the hours you
can run a generator.

If you end up getting one, please be considerate of your neighbors.  I
haven't run into it yet (knock on wood), but I'd be pretty unhappy to settle
in to a nice quiet campsite in an out of the way campground, just to have a
neighbor pull in and make me listen to their generator run for hours on
end...  If you got a quiet one and ran it for an hour or so in the middle of
the day to recharge batteries, I wouldn't complain...

For what it's worth...

Wesley

I can only give 2nd hand advice, but this is a friends experience:

They went from popup to travel trailer to 5th wheel over about 20 years.... they
bought a generator about 12 years ago and have regretted it ever since, for the
following reasons:

They rarely use it, most stays are in parks or in areas where they don't need
A/C, the main reason for the gen....

when they did use it, park quiet times and consideration of neighbors kept them
from using it at times that they needed to..

Adding up the times that they've used it, and the maintenance on it, it would
have been cheaper to rent one when needed.. (which is exactly what the RV dealer
that sold them the gen recommended)

It takes up space in truck and trailer and has to be protected against theft..

For their type of dry camping, mostly weekends or 4 day trips, they think that
adding 2 or 4 6 volt golf cart batteries to their existing battery would have
been a lot more cost effective and been used more often..

I researched them quite a bit, and the real winner was the Honda series..
"relatively" quiet, fairly efficient and easy to get worked on.. YMMV

mac

Please remove splinters before emailing

3KW will power your AC and small appliances but maybe not the micro at
the same time.
There's several look-alike chinese generators in the 3500W range that
retail for about $300.  For occasional use boondocking or for
emergency use at home, they're hard to beat for the money.  Oddly, it
seems auto parts stores like Pep Boys, Checkers are carrying these.
Most are rated at 68dB at 7 meters so are much quieter than the
contractor gens but not as quiet as the Honda and Kawasaki units that
sell for 5X as much.
Elim, PowerPro, Powerwise, Champion to name a few that differ mainly
in color only.  The Elim has a cool feature that with the flip of a
switch parallels the 2 110V windings into one outlet at 25A--great for
powering that big 13.5KBTU rooftop AC on a 5th wheel.

Chiming in a bit late but for what it worth it seems that most RVs use a 4kw
unit for single AC and 6kw for dual AC.  For an RV with single AC a 3.5kw
unit will probably be just fine as long as you don't run the any combination
of AC/microwave/blow dryer/toaster or toaster oven at the same time.

Jim