GENERATORS & 5 WHEEL
The Honda 3000 cannot be 'installed' in a trailer. It should not be run while in an enclosure. If you have a compartment big enough, you can cut a hole in the floor and winch the generator into and out of the compartment from above. Lower it to run, raise it to move. Have some boards which span the hole to set the generator on while under way.
My 3000 is mounted in the back of my truck, right behind the cab. I have a 1/3 fiberglass cover which protects it from rain, etc.
If the trailer and the bumper will stand it, you may be able to have a carrier on the back of the trailer which holds the generator.
If none of these options will work for you, you may want to trade in the 3000 for 2 2000 and the connection cable...