The initial goal was very well achieved.
I dislike the long cooldown, especially if one of your trucks was destroyed and you need to wait so damn long to set up your new one.
Suggestion:
1st truck: delay it for 3 mins
2nd truck: delay it for 4 mins (or 1 min after the 1st truck is set up)
3rd truck: delay it for 5 mins (or 1 min after the 2nd truck is set up)
Once an already built up truck is destroyed, a new one should appear instantly, or quite fast.