The pass-thru storage doors on my 315 don't leak, though they aren't completely waterproof, either. Those catch trays at the ends of the pass-thru (or whatever they are called) are a smart design feature choice by GD to account for this potential IMO.
The storage door for under the bed--that was (and still is) another story. I haven't permanently fixed mine (yet) but I know the problem.
The insert (the "insert" is the brown metal trim piece that stays attached to the camper) that the door closes in is the issue. Along the bottom interior edge of the insert it is not flush with the aluminum frame (but it is flush with the exterior wall). In other words, on the bottom edge (inside the storage area) there's an air gap between the aluminum frame and the bottom of the insert. I can feel this with my fingers when I reach in and feel along the bottom back edge of the insert.
When the screws were installed to attached the insert to the aluminum frame, the gorilla that installed them drove them right through the thin metal of the insert. This created gouges in the insert with gaps around the screw head and bent the insert down at a angle. When water collected in the down-turned insert, gravity directs it to pool and then it leaked through the gaps around the screw heads, entering the storage area.
As a temp fix I removed the screws, added silicone in and around the insert screw holes (and on the screws themselves) and then reinstalled. Before tightening I also bent the bottom of the insert up (gently!) so it is not so easy for the water to pool.
If all of those words make no sense, I can take pictures later when I get home from work later today.
-Howard