There's all the info you could want in the threads here.
Personally, I leave the boat rigged on the trailer and always haul it that way. Its pretty easy to get the hang of what to do going over passes - let a little air out before you head up the hill, put some more in when you get to the bottom. If it gets warm, let a little air out, if it cools off and you're driving somewhere, top it off unless you're going up the big hill - then it'll tighten by itself pretty soon.
When driving I prefer to have the boat pretty tight so the frame isn't bouncing up and down or popping against the straps holding the boat down. Strap the frame to the trailer if you're driving with the boat rigged.