I'd think you'd want the L14-30 (generator side) to 14-50R (rv side) adapter. Here is one:
http://www.amazon.com/Camco-55422-Po...14-50R+adapter
What I found when running 5000-6000 watt standard generators was that often the L14-30 (240V @ 30A plug) was actually overload protected at somewhere around 15 amps. This makes sense if you're actually pulling from both sides and don't want to overload a 5000-6000 watt generator, but when you've got a 30A trailer, you're only pulling from one side. It effectively meant that you could only use about 3600 watts. Literally it'd blow that circuit breaker if I ran anything other than a single AC.
Moving to a smaller generator (3200 watt, but only 120v - the Champion) that was overload protected at 25A @ 120V actually meant meant that I could get more useful power out of it. Yours is 3200 watt at 240V. You need to figure out how many amps the circuit breaker is on your 240V connection - it may be better to actually pull from one of the 120V sockets, depending on how it's setup.
Sorry if this is confusing.
What I'm saying is that unless your trailer balances the load well, you may run into the same thing, that a 5000-6000 watt generator doesn't provide the same power as a 3000-4000 watt generator that is wired for more amps...