A/C and Heat

[SFTorange]

Hello,

I've been reading a lot of posts lately about air conditioning, and I can't seem to find an answer to this question. I've looked into Old Air and Vintage Air, but I am really concerned about the functionality of the heaters in these systems. I live in Montana (where it's currently 5 below), and I worry that the heaters on the aftermarket a/c units are just an afterthought. I've also noticed that the aftermarket setups don't bring in outside air either which can wreak havoc on defrosting.

It seems like a factory system could solve some of my problems, but I worry about the time an expense to install a factory setup.

Thoughts?