If you are going to be all over SD then you will need all the towers, if just in a certian area just put in the ones close to you. We camp a lot up there but we only have the towers that we will be travelig through. If there is no signal from the tower the scan blips past that tower anyhow, so if you want them all no problem, just a little extra time programing, if you don't want to scan the towers just lock them out, very easy with the 996.
Ted