The smallest AC is about the size of New Computer.

Pretty small and light weight.

But, they still create heat and need to be vented out.

If you have a grow box, the situation remains the same.

The incoming air will :

a) need to be cooled by an AC unit, or
b) need to be cool as it enters the grow box.

If you have option b, as in say inside air conditioned temps, you just need a good strong inline fan to suck the hot air out. But then again, you need to vent it somewhere, otherwise, you will heat the outside air and start sucking in the warm air again.

A vicious cycle yes?

I have a 6' X 10' trailer at the office that I am gonna park in my garage for my next grow. THis no room shit sucks bad.