DS2: special armour on light VTOLS?

Would it be legal to put special armour on an armour class 0 vehicle in
DS2?
I'm thinking of a size-1 VTOL, which isn't allowed any armour, with
ablative
protection to reduce the risk of being plinked by HELs at long range. 
Is
AC0 simply "no armour of any sort"?

Rob Paul