How much rain water is pooled on top of the cover? If there is none, I would suggest that you attempt to remove the cover and store it until you get home and can get it fixed. Had a problem with one of mine last year and had to get a new spring assy for it. On each end there is a hole for a cotter pin to be inserted. I used a 16d nail. Close the slide, insert the pins and unbolt the hardware from the slide. Slide the whole thing out of the gutter and store it. While it does take two people to make it easier it only takes about 15 minutes to get it off and stored. If you cannot get it off where you are parked, then get a couple of really large cotter pins or two 16d nails, bend one end 90 degrees and insert them in the holes on each end. Then bend the other end to prevent them from falling out. Just don't forget they are there and attempt to open the slide. Otherwise you will have way more than a broken spring to deal with.
Don and Lorri
2007 Dodge 3500 dually