I'd suggest to test the whole trailer. There may be the possibility that there are other failed sealant spots. I use a 1/2 HP furnace blower sitting on a step ladder, sealed into a window opening with cardboard/plywood and tape to DIY the pressure test.
The squirrel cage pushes about 1000-1500 CFM. With even the simplest blocking of the built in egress points like vent openings, windows, furnace ducts, etc, I'm able to develop 1" rise in water column on my DIY manometer. I could block off nothing inside and the blower would give enough rise in pressure to fulfill the testing.
Others have used leaf blowers, rug driers, and some even say their vent fans will do it. A lot depends on area and the extent of the seal of the trailer.