Unfortunately there isn't and won't be a folding cover on the market that is 100% weatherproof, rather you will find they are weather resistant.. being in the industry for about 10 years (Undercover - FLEX and then BAK) I can tell you this has and probably always will be an issue. Things I've seen in the past is customers using clear caulking around the "leak points" on the rails along with making sure the drain tubes are properly installed and etc.Geesh. This whole thing feels like they just don't have covers for the rambox version nailed down 100% yet. I'd love to get a cover sooner rather than later, but I think it may be smarter for me to wait until spring. By then maybe more covers will be available and I can see which ones are having the most success in keeping rain out and installing easily.
IF anyone needs additional help, let me know! While I do work M-F 8-5 at another company now I still enjoy helping with these covers as it was a part of my life for so long. (Only being 30)
Have a great night!!