how about armor hull?

[GooglyBoogly]

but some of those skills create units, which can deal less damge from armour.

The more expensive tanks already get pretty decent armour- I don't see a need for additional armour packs that can be added to any tank.

Remember, we already have many creep-only weapons, which could be considered to fill the role of armour boosting items (why take less damage, when you can just kill the units instead?)