5er Generators
If your trailer has a compartment which is or can be set up for generator usage, that is your best option. Generally the standard here is Onan, although some other companies do make models which may work ok. Noise can be a nuisance, but your real concerns should be not filling your trailer with exhaust, or overheating the generator enough to damage it.
For 1 A/C, 4K watts should be enough, 3K can do in some cases (may require installing an 'easy start' kit in the A/C).
Generators in the bed of the truck are a pain in the butt, but with many 5ers, the only practical choice. That's where mine is, and after considerable searching, I found a fiberglass 1/3 bed cover which keeps it out of the weather and prying eyes/fingers.
For standalone generators, Honda EU (inverter) series are the standard. A bit pricey, they are perhaps the quietest of generators, fuel efficient and provide power as clean as, if not cleaner than, the power company. The EU3000 is marginal, big and heavy, but a pleasure to use with its key start. Many people use a pair of EU2000 connected by a synch cord. This provides all the power you are likely to need, in a small, light, easy to store (and steal) package. EU2000s can even be stored in 5er compartments between usage (as long as any gas fumes can't leak into the trailer).
One thing to consider, if your generator is mounted in the bed of your truck, you may want to rewire the trailer with that in mind. Properly set up, you could even run the generator while driving, allowing for a cool trailer when you stop.