Not sure if the installation details on a motorhome differ much from a trailer, but quite a few trailer owners - including me - have switched from the cheap and nasty skylight that Airstream originally installed for far more substantial polycarbonate/aluminum custom made units made by this company.
Maxim Skylights - Hurricane, Hail and Impact Resistant Skylights
My original skylights were badly deteriorated and leaking from a multitude of cracks where the securing screws go through the flanges.
The new units are a fantastic improvement - they also meet certain standards in Florida for hurricane / hail resistance.
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.