This article covers the support for Ambush mode.

Short summary - similar to RvB, only with a slightly different primary goal, attackers 'set an ambush' and defenders have to get to a checkpoint.

As always, please create fun maps (now with Ambush too) which would bring fame to your name.

Now the syntax part. Mainly it's the same, only you need to put special_map_type="ambush" into options like

<Options timeH="10" timeM="10" weather="0" armour="false" interior="0" friendlyfire="false" show_blips="false" show_radar="false" special_map_type="ambush"/>

Also, you need to define the place where the Convoy heads to. Since Convoy is a defender, it should be put inside Defend tag like this:

<Defend posX="2227.5258789063" posY="2452.0656738281" posZ="10.866348266602" skin="287" rot="0" weapons="34,10;24,20;28,200" message="Set off in a convoy and head to Las Barrancas, at least 1 barracks must survive."  >
	<finish_marker id="Convoy target" posX="-808.97088623047" posY="1556.0676269531" posZ="26.9609375" vehicleType="Barracks"/>
</Defend>

Id isn't needed, but is there for your reference.
positions (posX, posY and posZ) are self-explanatory.
vehicleType is the type of vehicle which must reach the checkpoint, this is the vehicle type that the Ambushers have to blow up. You can use either vehicle ids or vehicle names.

Also, note that you can add as many vehicles as you like.

Only the vehicles that are entered at least once are the target of the Ambushers (eg you can leave a Barracks at LVPD, nothing happens and round end will be triggered still)

The attacker tag is still required, but as it's standard, it's covered in the RvB map topic here

Have fun and create great maps!

The server has a map, rvb_Ambush_Original (from which I took these examples), which uses this mode of RvB.
Both the rvb_Ambush_Original and the ambush mode is quite likely might contain some bugs, so all bug reports welcome.