I'm not sure I am can describe this well. And, it will be difficult to take pictures. So, I will do my best.
The rubber seals are not the primary way the water is kept out. They do seal against rain and there are usually two. The one that is easiest to see is called the "wipe" seal. It's primary purpose is to work like a windshield wiper to wipe excess water off when you retract the slide so the rug doesn't get wet. It also deflects a lot of rain, but is not an absolute seal against it. The more important rubber seal is like weather stripping and is squished between the slide lip and the sidewall. There are two sets. One for retracted and one for extended. They are difficult to replace and, over time, the slide adjustment can drift so that there is not even contact all the way around. I'm not convinced that all coaches can have this seal work perfectly.
The best way to keep the rain out is maintaining the slide roof itself.
If the slide were all the way out of the coach and you were looking at it from the end, the top would be a wide "U" shape. The vertical parts of the "U" are about 3 inches. The outer one is easy to see when the slide is extended and the inner one has decorative molding on it inside. The bottom of the "U" is flat, made of metal sheets and there are rivets. Each of those seams, the rivet heads and the joints between the flat area and the short vertical parts of the "U" are prone to leaking and the sealants have to be maintained. The exception to this is the version Beaver used until Monaco took over. The roof was fiberglass and has a deep gutter built in.
There are two ways to gain access to what needs to be sealed. You can extend the awning and "C" clamp blocks of wood to the fabric so that it does not roll up. Then remove the brackets that hold the roll up mechanism. I attach ropes, then lay the loose assembly on the roof and then creatively tie it so it stays there while I work. The other way to gain access is to do the same thing with the clamps, leave the brackets on and work under the loose fabric like it was a tent. It forces you to work from the ends on a ladder or on your belly (on top of the slide).
It is important to mention that the roll up mechanisms in these awning can eat fingers. Painfully and permanently.
There are two ways to seal the inner seam. Under warranty, a tech did my kitchen slide by retracting it 6 or 8 inches. He fit a piece of clear plastic tubing over the end of the sealant tube, and by feel, ran a bead of sealant along the seam. He worked in the narrow gap between the ceiling and slide lip. The other way is to do it from the outside. I use small wood blocks to hold the wipe seal out of the way and can reach the seam with the nozzle of the sealant tube. There is some risk that you will have to clean a little sealant off the wipe seal.
If the awning is out of the way, the seams between the flat top sheets, the seam along the outside vertical lip and the rivet heads are easy, except for getting it clean first. I use acetone. It will dull the paint but it is the top of the slide and not visible.
Many say not to use silicone because the second time your do it will be difficult. My Beaver came from the factory with silicone everywhere. I don't know what the best sealant is.
Good luck!
