I finally got my driveway gate installed. Took me a bit longer to find the right hinges than I thought.
I started with nice 6x6 pressure treated posts (holes down 42" inches, each filled with six 60 lb bags of regular concrete). Each panel is comprised of three layers. Inside layer is 1x6 (4' height) panels, with 1x4 trim all around.
After building them, I was really surprised at their weight. I knew they'd probably weigh a bit, what with water seeping out of the wood when I screwed them all together, but even I was taken aback. About 180 lbs at first. After about 3 weeks drying in the basement, they lost about 20 lbs each.