Nice concept, however the M3 HT alone is not going to be enough, you already have the ambulance and while it needs to remain static and in friendly territory as well as having to lock down in order to heal units it's going to be a lot more cost effective in the long run considering that the M3 takes up a commander slot, doesn't provide much more Armor and so on.
However if it were to be the Mech Company M3 Assault Group then it would be much better considering it also has med packs and the Assault Engineers, but then again the Assault Engineers already have flamethrowers so there would be an overlap with the RE Flamethrower upgrade, so maybe this would be a perfect opportunity to introduce a Crocodile Sherman that can switch between shooting flames and real rounds?
Thanks for Ur reply.
I'll fix it based on your feedback.