Look right above the area you have circled. There appears to be a seam in the frame that goes around the door. I would suspect that seam.
Water could be getting in through or behind that seam, where it would drip directly on the top edge of the door. From there, depending on which way the trailer is leaning, is where the water would run.
I had a baggage door leak, that went back to the dealership, four times, and they couldn't find it. I did similar to what you did. I layed in there with a flashlight during a heavy rain. CWhat fixed it was pulling the door (frame and all) out of the trailer and replacing the putty tape between the door frame and trailer wall.
That mobile tech, probably has the capability and might have the materials with him, to do that kind of repair. It's not complicated. But, without having prior knowledge of it, he may not have the time in his schedule for tomorrow. Definately ask him to take a quick look. Maybe, he will have the time.
If you pull the door to replace the putty tape, install the new tape with no joints or seams accross the top of the frame. Any joints / seams in the tape, should be on sides or bottom. Preferrably the bottom.
For future reference, only places on a travel trailer, where one might use silicone, are in the shower, and around the sinks. On the exterior, silicone doesn't stick well, will not stand up to the weather, and it leaves a residue that prevents other caulking materials from sticking. That residue is difficult to clean off.
18 Nissan Titan XD
12 Flagstaff 831FKBSS
Wife and I
Retired Navy Master Chief (retired since 1995)