Okay, this doesn't appear to be a repost so please don't blam it down.
Here's how you mount on the zeppelin!:
1) most obviously get on an zeppelin first of all
2) go to the middle "hood" area and face the stairs that down to the lower parts of the zeppelin
3) do a jump aiming into the side of the hood so your standing pretty much "in " the hood and the upper deck
4) Use your mount and lo-behold there is no can't mount here error!
Have fun.