I had a bedroom slide that leaked at the lower trim on the outside wall.
Rain ran down the outside of the wall til it hit the trim at the bottom. Went behind the trim, then wicked between the inner and outer floor panels and ran out at the inside rear corner onto the bedroom carpet.
We resealed at the top seams two or three times before we realized that it was the lower area that was letting it in.
Painted the seam with Lanco (brand) elastomeric Roof paint and it has been good for a year now (including some really hard rainstorms). I watch for travel vibration induced cracks in the paint, but have not seen any.
Lanco is available at Home Depot.