Yeah, I had a lot of roof leaks to deal with last summer.
For a roof leak: Remove the plastic rails and look for cracks in the seam where the roof panel seam is. I had several. When you're done sealing that up, I suggest getting some putty ...rope caulk (hardware store) or even plumbers putty works well and make a little doughnut to put under and around the nuts when you put them back on to keep water out.
Also, it could be a leak at the rear-door top gasket too, ..or cracked seam sealer on the upper rear corners. The pinch portion of the top rear door gasket can rust and flair out (not pinch very tight). I wasn't able to get mine tight enough so I bought a new one. Even then I had to use a non-hardening bedding compound (3M product) on the pinch of the new gasket. All that did the trick.
Check under the carpets where the rear passengers feet go. Probably soaked under there. All the interior plastic is super-easy to remove ..and the metal clips are reusable. The interiors are put together nicely on these H3's.
Good luck.
