Here are a few pictures of the problem.
The seal consist, in fact of 3 seals, one black outside, one black inside and one white inside.
The problem is created by the friction between the white seal and the interior black one.
Here is what happened: You open your slide out, it goes out and out and out till those 2 seals comes in contact THEN, your slide out goes DOWN to settle. The black seal is pulled downward and because of the poor retention system, it just doesn't hold.
The retention system is a simple nail tacked thru the rubber, no washer, no large head.
My black seal is now ripped on 4 nails and partly hanging outside. The white seal is ripped 2 nails.
My suggestion is to pull the seal back in place and screw it with large washer.
Also, to help future damage, I suggest to silicone spray (or graphite) heavily those two joints.
I think sooner or later, all slide out built this way will have broken seal.