Wagon / APC and AT Fire

[Poor Yorek]

Am I right that I can not use AT fire against wagons or APCs ? That´s how I read the rules, but it seems a little bit silly 

One may use AT fire against any unit that has an armor value, even if that value is -1 as for a truck.  Whether a wagon has such a value is the question underlying Peter's post.  

I have to add that the truck's armor value of -1 is wonderfully nostalgic of the old D&D negative armor classes (which, in turn, were great ways to teach a kid how to add and subtract negative numbers).