My suggestion is to go with "Supersprings" the add-on leaf spring that's easy to install by yourself, I looked at air bags and talked to a few people that had them and they said that if they had it to do over again they would install Supersprings, when I asked why they said that you had to keep a minimum of 3psi in the bags at all times and then there were those that said they were afraid of getting a leak and that it was a pain to keep checking the pressure to make sure that the minimum psi was still there and that they leak down. I don't have either on my Tundra but I have looked at both and listened to others that had used both and I think that if I had to choose I would choose the Supersprings. Here's a URL for the installation of Supersprings:
http://www.truckspring.com/video_1072.html my take is that the spring idea would be a lot less trouble, is easier to install, and does not come into play untill you load the bed and it needs the extra lift, so this is just one more option for you to consider, JMHO.