For its later incarnation I didn't sand it or anything; I just used the same techniques to stand it up in a bucket of dirt (using cans to keep it upright and balanced) and painted it with a coat of primer. Hardly high-tech, but it worked.
(That's a kitty litter bucket. They come in very handy for many uses.)
When the primer was dry, I began adding color. I used four colors: gold, turquoise, purple, and red, so I just started with gold and counted the sections, painting all the gold first, then all the purple, turquoise, and finally the red.http://morning-glory-garden.blogspot.com/search/label/shade%20house or somewhere in the front entry http://morning-glory-garden.blogspot.com/search/label/ferns. In either case, it won't be subjected to the harsher elements as much as it was in the garden, but it will need more protection than just paint can offer.