Diagnosing leaks is not exactly a science, though there are tools and tricks that can help. One such trick is the light test. At night, close all the blinds and turn on all the lights, even those in the storage areas. Sometimes light will appear though openings and you can find your culprit that way.
IIRC, the 22s of that year did not have belly pans, so you may find it far easier to find with a light test than we folks that have belly pans.
If you can't see any light, grab a very bright flashlight and try again from the inside targeting specifically in areas where you think it might be coming in.
If still no luck, try the opposite, get some halogen floods and shine them into the trailer from under and around the trailer from the outside at night, with all the interior lights off. There you may find areas letting light in, which may also let water in.
There are positive pressure units that can be attached and you spray soapy water on the trailer after it's turned on, these produce bubbles where the air is escaping. The tool is called sealtech I believe. Many RV repair places have these or something similar.
Also keep in mind that some leaks can travel, meaning that you may think it's coming from place "A", but later find that a vent pipe seal on the roof is bad, and the water is traveling to a place totally away from where you think. This is where the sealtech machine comes in handy.
Last idea is to let it dry, and simulate the issue with a hose. This is how I found that the factory did not put any caulk in one of my wheel wells. My trailer failed every light test I described above. It would rain like hell and no leak...minute I towed in rain, water in the trailer.
Just a few tips and tricks...hope it helps and good hunting.