I've had a Superglide for years in a short bed pickup; it works perfectly. I've got at least 30,000 miles of towing using it.
1) I do not keep it covered.
2) My Superglide uses a graphite spray paint on the rails. The only maintenance done frequently is to spray a bit of that paint on the rails and that is usually at intervals of every two or three towing days. Takes five minutes max.
3) Other maintenance I do is annual and not difficult, just general cleaning, oiling, and an occasional adjustment.
4) There is no other hitch I'd rather have than my Superglide.