Eddie, I like your testing idea. My neighbor is trying this, too, but in addition to the light exposure he is walking on it every day in and out of their home! It is still holding up. I hate to get too excited about it, but would LOVE to find out that this color and product will last a long, long time.
Victor,
I've found that Minwax makes a product called Gelstain that you can buy just about anywhere. It's designed for fiberglass and metal doors to make them look like wood. Then you put a finish clear coat over it to protect it.
My tests looked really good on the Hardi siding.
I built a gazebo for our hottub over the summer and put the Hardi lap siding on it. Then my wife stained it with the Minwax Gelstain and sealed it.
Thanks for sharing your pictures and tips on staining the siding. It's only been a few months, but so far, it's amazing. Everyone who's seen it thinks it's real wood. Even after touching it!!!!