If you are talking the slide seals on the sides and top of the slide, if you have to replace them every year, that is a problem. Or if you have to replace sealing tape on the slide every year or 2, that is not normal either. Something is not correct. I went 10 years on my first set of slide seals and that was due to a screw head beating through it. The butyl slide tape after about 6 years I did change it to Eternabond as the top layer of the standard slide tape was coming up. But that did not cause any leaks I changed it as a preventative measure.
All slide seals are not the same nor the same configuration. Nor is the way slides are built. Pictures of your slide seal setup would be helpful to show us what you are up against. And that slide seal tape you are replacing. We may be able to spot something you can fix. Take many pic's showing the whole slide, then the seals and get down on the ground and take pics looking up with the slide out how the seals looks sealing against the camper flange.
My slide has no topper and I have never had a leak in the slide in the 11 years of us having this camper. A topper does help but if that is your main roof to prevent slide leaks, that is not good.
What year, brand and model camper do you have?
Hope this helps
John