We've had slide toppers on our most recent three TTs. The first one, nearly 30 years ago, had no slide. I definitely like our toppers, which keep much of the rain, pine needles, sticks, etc. off the slide-out roof. The current TT had its rather large toppers installed at the FR factory, and the topper on our previous two (SOB) TTs were installed by the dealers. All were installed with proper tension and gave us no trouble at all. On the other hand, our best friends and camping buddies had a topper on their previous TT that was installed too loose and they used pool noodles under the topper to prevent it from forming a large "water trap" when it rained. They've had no issues with the toppers on their 2019 Rockwood. Your dealer should guarantee its work, and hence should make it right. Good luck with the call!
Chris, Paula, & camping Labs, Shasta (RIP 8/10/20) & Cammie
2005 Yukon XL 2500 with 8.1 Engine, Allison Transmission, and 3.73 Axle Ratio
2019 Rockwood Signature 8335BSS with Hensley Arrow Hitch