This is not HWP "recovery time" as requested by the OP, as I don't think that is doable right now.
But I have already implemented the idea of recovering tank corpses and repairing them (along with more tank weapons and alloy ground tanks) in the XAE (Full collection of XAE mods and resources in its own thread). For reference on how I did it, see the attached file.
As far as I can tell, it is the best solution currently. Instead of boosting armor to make tanks useful (the vanilla tanks are pretty meh), it makes losing the tank less of an issue, so you recover from the loss faster and can keep using tanks.