Frank,
You may want to check your slide seals too. An extended slide shouldn't leak, topper or no topper.
When our kitchen slide is our and our awning is not it use, there is no topper of any kind over it. Water intrusion has never been an issue.
My TT has no slide topper either, and there is no water intrusion when it rains either...any more. Having said that, it sure wasn't right from the factory. I bought it as a project and did a
complete rebuild. Part of that rebuild was fixing how the factory had "sealed" the slide. Their "seal" acted more like a funnel. :B