I"v been in a situation that:
1 was transporting clay in my wagon.
2 player (newly spawned) runned into wagon
3 got back to my claim that unfortunatly was on the limit of the walls and gates were closed.
4 he stays there just waiting for me to open the gate and steal the wagon

As i'm just a hermit and do not build my way up to rage yet i could do nothing as an stranger jumped in my wagon and just had to kill my pattience to get it from me while i was riding it.
*Maybe an "u cant enter and ocupied vehicle" would solve problem for ppl without thiev or trespassing ? (Best)
*Or let us to operate simple things as gates from the wagons (not very good)
* allow only party members to ride your vehicle, but make it so the player is still vulnerable to pvp while inside (maybe let them ride the vehicle only after ir had aggroed its target)
Really Really sorry for my english