SF: i don't remember you showing any pictures of your ship lap or siding material other than after you put it up on the walls. if you did i'll look back through the thread or can you post up a few and are they notched on each side to slip on top of each other? i know you said they are shrinking, but i don't see any daylight so even though you are siding over them they look awesome from the insides.
also are they 8, 12 or 20 foot long and 2 x 6's?
i bet your arms and back are sore so you might want to buy a Teeter Up inversion table at Costco next time you are there because mine has kept me from taking advil for about 8 years now.
here's a thread about inversion tables in case you don't already own one.
http://www.garagejournal.com/forum/showthread.php?p=5090065#post5090065
cheers and keep up the great work and that back wall is going up quick.