Had a similar issue. It leaked onto the top of the slide (while in) and dripped to both ends. I ended up realizing the trailer was canted to the entry door side and exposed the top slide seal side to the rain. I couldn't find any other reasons it was leaking inside. Once I adjusted the trailer to be more level side to side it didn't happen again.
'14 Sunset Trail 290QB
Towed by a '15 Ram 2500 6.4 Hemi 4x4 CC
Equalizer 1200/12K (just because I still have it)