Ok..... there is a topic here regarding a mod to built up the lower edge of that access hole. Can you see/reach the gap from the exterior? If so, decor (non-sag the heck out of it)
Come on forum, help us find a link to building up the lower edge to keep the water out.
I think it was a track or L angle?
2011 Coachman Freedom Express 295RLDS- Sold
2015 F-250 FX4 SUPER DUTY 6.2L Gas 4WD SuperCab XL 3.73 rear / 158" WB / 8' bed. Factory anti-sway and brake controller