I have owned the Roll-N-Loc, The PE Jackrabbit, and currently the PE Bedlocker (electric).
All were/are great. I'm in Manitoba, and have winter about 11 months of the year (at least that's the way it feels sometimes
How do they perform in the winter - Terrible! but I love them. My current one is the worst of all in the winter, but will get the same unit in my next truck. Snow load is not an issue, they all handle it well. I recommend sweeping the snow off it before driving anywhere to reduce the snowbank on the back window, as the heat from the window will melt the snow and make ice.....roll tops and ice are not the best of friends.
In the extreme cold, you can open and close....a bit stiff, and may not open 100%, but still works. The problem is when the temp is below freezing, but the sun shining on the 'Black' surface makes just enough heat to melt the snow at the canister opening, and it flows toward the canister, gets to the shade about 1/2 inch in, and freezes solid. Sometimes if you catch it soon enough, you can slap the top with your hand and break the ice. If the ice is too thick and doesn't break using this method, then opening it is NOT an option, and the only remedy is to take it into a heated garage long enough to melt the ice and dry completely.
My current one has an all metal top. When it 'sun melts', it freezes every slat....and there is one slat every 1-1/2" from the tailgate to the canister. There is no 'slap it with your hand' option here....the heated garage is the only solution.
BUT, even though I have not mentioned a single positive thing, I AM on my third roll top cover, and my next truck will have one too.
Masochistic?.... Heck no.....if I was that, I'd be driving a Toyota!