I sat in my trailer during a month of thunderstorms on a farmer's milk stool with a poacher's light, mapping leaks. I found and fixed 11 leaks from the entry door to the front of the side window that's directly in front of the entry door. That's a relatively small space.
There were other leaks, but the prolific leaks were near the entry door. The hardest one to find, was a outside skin lap corner. I had to remove the inside skin and insulation to find and fix that one. I found that one during a thunderstorm about midnight one night.
The last belly pan leak was the step release slot. That one leaked a LOT, and I couldn't fix it. I ended up creating screened drain holes in the belly pan as a way for the water to drain out.