From personal experience, you dont want them in areas like attics because it gets to darn hot and dry, and the planks will dry to fast and check like crazy! I put mine in the back of the garage off the floor with 1 X 2 strips, and stack evenly space for air to get all the way around them. Stack'em up and let'em go for a few years. They will be real nice.
I used to paint them, but I have better results now with parafin wax. Melt the parafin in a big enough pot or pan, and with the help of a friend, dip the ends of the planks into the melted wax. Let sit in the hot wax for 20 seconds or so to open the pores of the wood, and then remove. Works great!
BE CAREFUL MELTING PARAFIN WAX with flame! I use a hot plate!