I've made a siege tower with drawbridge down animation (see models gallery - first models)
I've got a modified blimp working perfectly as a siege tower in the game but I don't know how to connect my animation with the unload ability - so that once you unload the drawbridge stays down
This probably could also be changed in the ability's coding. If you go look in the SLK files, alas I think its there, you will see that it mostly plays the casting animation but I think you can change that.