As promised wanted to report back on how the Rage Sports Waterproof bag (link provided in an earlier post in this thread) worked for us (used it for a ski trip to the mountains for our family of 5, 6 hour journey each way)...
Overall we were very pleased with the bag. First of all this thing is huge, 19.6 cu feet of storage, 59x24x24 so it filled the bed lengthwise and took up about half of the bed width, height was perfect for the ridge. Loaded it up with 2 medium sized rolling suitcases, 2 medium sized duffle bags, 1 large plastic tub, 1 18x24x12 food bag, 1 large duffle bag and 2 backpacks and still had room to spare. Very impressed with the capacity.
Bag seems to be made of quality materials all except the tie down straps on the top of the bag, they looked a little weak so I did not use them and just used 14 ft ratcheting tie downs wrapped around the bag attached to the bed anchor points. Zipper was heavy duty, a little tough to get it zipped around the corners even though we did not fill the bag up, especially in the cold and snow when packing up to come home but no significant issues there. There is a 2 inch flap that pulls down over the zipper and attaches to the bag with Velcro, seemed to seal it up pretty well.
Had clear, dry weather on the way up but the morning we were packing up to leave had about 3-4 inches of snow followed by rain as we got further down the mountain. When we got home everything was bone dry, no signs of leakage. I could see how maybe in a torrential downpour at high speeds you could get a little leakage up under the flap through the zipper but can't imagine you would get enough water in it to actually get anything wet. Thus far very pleased with the purchase, it certainly served its purpose.
Between the trunk, the bag and the under seat storage in the back we had more than enough room to pack for a family of 5 with 3 young children, luggage, food, skis, coolers, etc. for a 5 day trip and amazingly had room to spare.
Here are a few pics, not the greatest quality but will hopefully give you an idea of what it looks like (most of these were taken when we had it about 1/2 packed). While I haven't had a chance to test it in heavy rain based on my initial experience on this trip I think it was a good buy and would definitely recommend to anyone looking for something similar.