Well finally got to the August story mission Defeense of Lanseal really stuck on it guess I can't deal with this many V2's
First off, Avan needs to run away from Dirk, go and capture the base in his area, bring out something to slap the supply vehicle, and then you can deal with him when he follows you. (it really helps if Avan is a Fencer or Fencer Elite here)
Park Armor Techs in all your key bases, don't need to be special fancy ones, plain ones will do. Armour Tech on sandbags is dug in deeper than an alabama tick, without supply vehicles even a V2 is not going to make them budge.
Use Fencers (Inghild is the best bet, very large number of +vs. personnel boosts that will tip her over and allow her to 1hit the V2s, because with 4-5 chances it's a good bet at least one of them will activate. Troopers can do the job but are much more vulnerable to interception fire, whereas Fencers will laugh it off even from V2s in the front arc.)