John, it'll depend entirely on which and how many appliances you have running simultaneously in that trailer. Just a basic rule of thumb: 30 amps times 120 volts = 3600 watts. When we lived in a 32' trailer, I had a 4500 Kohler running on LPG, so they tell me you lose 11% converting from gasoline to LPG, and I wanted a 4000 watt generator; never had a problem running the clothes dryer, air-conditioning, TV, and coffee maker at the same time.
Yep, that ought to do just fine. I don't know what size your A/C is, but it won't be too big. We had a 15k BTU unit on our trailer. And in '73 we used to run a 10k BTU A/C on a little Winnebago with a single cylinder 2500 watt Onan.
Start up is your biggest obstacle. A 3500 watt generator won't hardly start capacitor start type motors over 1.5hp. For your situation, getting the AC going will be the test. Most generators have the ability to put out an excess of the nameplate rated watts for a short duration.
Of course you're right, Bill, but I didn't go into that because he said "travel trailer" and that was my principle hobby for a lot of years, so I know he ain't got any 220./w3tcompact/icons/laugh.gif
Remenber that most generators are 'marketed' with their peak wattage. eg. most 3500w generator can only be run at 80% of their rated 3500w peak load continuously. Look for the Load Factor (LF=0.8 means 80% sustained) or words like continuous duty. Some really cheap generators have 50% LF. Comercial generators like honda's indistrial line are rated at 100% LF. Thats why they cost 2x the price. The best method is to add up the needs of all you appliances, including starting currents, and choose the right generator accordingly.