Or 9 troops. Then you could actually use jeeps for captures!
You can use jeeps for captures. Just take four jeeps. If one gets killed, make a second run. If you are fast, you should be able to make a second run with a jeep and still get troops to the map room in time for the capture.
If I remember correctly, each trooper counts as damage against the map room. It has a repair time, just like any other item, but I don't remember the repair time.