making "scenery vehicles" respawn?

[JimmyBeGood]

i'm making a multiplayer mod for boarding action, and on the top of the ships I have a ton of vehicles that i put into it by changing them to scenery in HMT. my question is, hoq do i make it so they can respawn without getting exception errors. i'm not sure if this is where this should go so please dont yell at me if this is in the wrong place. thanks in advance if you know how to do this