My Hi-Lo seals that gap at the top of the tip out (when it's folded into the camper) and the top half is in the down position.
When I first got my Hi-Lo, I was working in it getting it loaded for our first camping trip (so the top was "up", but the tip out was "in" and the exterior cover was "down".
I saw that gap and thought, "What idiot designed that?".....because it had a huge gap. But, when I let the top down, that gap is sealed..at the top of the gap. You can still stick your hand into the gap at the bottom, exterior of the camper, but it's sealed at the top.