Some vehicles are just props in the static layer. These you cannot hide, so make sure it is from the dynamic layer. As it is dynamic, you could blow it up, so have to make it indistructable.
Just add a basic hemtt or m1078
start game
<element type="ActivateVehicle" vehicle_id="blocker_01" start_time="2.0"/>
now I think you need to SetSlot here and change it to make it indistructable, have to check this bit.
But when needed:
<element type="RemoveVehicle" vehicle_id="blocker_01" start_time="0.2"/>
Noted post above, good to know.