A couple of points. The portable unit requires an exhaust vent (the hot air has to go somewhere). Not sure how you would manage that in a trailer. Secondly, when is the last time the condenser coil was cleaned on your unit? Inside filters also. These can have a huge impact on performance. But 100 w/ sun beating down is a tall order for a 1 ton+ unit. If you had a portable thermal gun you could verify the intake and output air temp and post back. Should see at least a 20 degree delta.
We have a 15K unit and it performs great in the Texas sun. Never regret the upgrade.