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A few pics of my roll n lock. I've had 3 and they've all been good. Locks in a few different positions and onto the tailgate. Fairly weatherproof, but a little moisture gets in from the sides and around the tail gate since I don't have a tailgate seal.(too hard to clean out when I haul dirt,gravel and bark mulch) takes a little maintenance to keep the latches from freezing in the winter. My neighbor has a retrax pro with the metal slats instead of the vinyl cover over aluminum that mine has and it's a lot harder to open in the winter with our humidity it seems to glue all the slats together with ice. His is just as weather tight though. 
My $.02. I have the bak fibermax on my 2013 since new. I got the cover because I wanted some extra security for bed contents for trips (hard cover vs. vinyl). I can never keep the bed dry even after making adjustments on the rails (my brother has the same issue with his Silverado and he had his replaced 2x). Its not much water but it seems to get in. After 4 years now the rubber seals on the rails are all cracking because of the age and seasonal temp. changes. The tailgate seal occasionally freezes to the tailgate also (not a big minus). I take a shim and run in it down the length of the seal and its free.
What do you think about the poly carbonate? I would like to save money but want to be sure it is sufficient. I’m not familiar with it.....I went with the Retrax One MX retractable tonneau cover after looking at a lot of reviews. The "One" is a polycarbonate construction as opposed to the all metal of the "Pro".
It fits my needs just fine. The "MX" means the finish is a matte black. If you get the non "MX" it will be gloss black finish.
I'd strongly advise you also get a tailgate seal as the gaps in the tailgate for water penetration are substantial. I went with the Extang MaxSeal....
) and even though the sides dont stick down all the way because the velcro is faded white, but each time I go through a car wash no water gets into the bed until i roll up the cover to where only a few splashes make their way in, but as far as rain and snow have gone, nada, now dust on the other hand always finds its way in.
