Hmm, if not done right, I think your players will dislike the railroad structure of the setup.
I would stage it in the following way (as an example):
GM plan: a total of 4 ambush encounters are planned as well as 3 major encounters
Briefing: the players must escort something (vehicles?) through a city and are warned small scale ambushes are likely. They are ordered to not halt and fight it out as that will not only allow the ambushers to bring all their meagre weaponry in play from a superior position but also allow other enemy squads/warbands/rebel groups to reach the fight and join in. Speed is their best defence...
Typical Ambush: The column leader or main scout has to make an opposed awareness or other applicable skill (command, tactics etc) to spot an ambush. The ambush is typically a small affair (or otherwise it would have to be played out by the players) with a few men taking potshots and lobbing grenades etc. If the column wins the opposed test, they spot the ambush and get to pour fire into the ambushers (who still enjoy some cover) before speeding through the ambush and only receiving some scattered fire. Score one point for the column.
If they fail to spot the ambush, the ambushers get shot at a lot and must make a dodge/toughness/whatever roll to remain unwounded. If they make the roll, the next time at the next ambush a cumulative-10 penalty is added (luck is running out). As soon as they get hit and suffer 1d5 wounds if you are mean and 1 wound if you are not, the penalty is reset to +0.
1) they encounter a previous column which halted and was destroyed. Enemy forces are looting the vehicles and killing/torturing/eating the few survivors.
2) The road is blocked by the enemy with broken vehicles, debris etc. The column must fight its way through to continue and reach their destination.
3) A broken down vehicle with friendly forces needs their help. Perhaps with a senior officer. Of course they are disguised enemy troops and are to distract them and halt the column before springing an ambush.
That way there are encounters the players can act in and encounters that just set the mood while still allowing them to use some skills and (hopefully) take a bit of damage.
Edited by ranoncles, 06 February 2014 - 03:01 AM.