There, some suggestions already. I cannot comment about what is best without seeing the structure. I have used foam in many ways, it is the best bang for the buck. Spray foam is just plain awesome, but so is the cost. BUT, if the alum. is the roof structure, as Greg suggests, it would take an act of Congress to get it off once sprayed in place. You might have to replace it someday.
I am not sure about the condensation thing, it will form wherever the dew point sets up, which may be around a window or sidewall if there is much and it cannot vent or form on a larger cold surface. I like to use foam and leave a place for the house to vent, rather then invest in a heat exchanger. Drywall is cheap, pull down the 3/8, put strips of wood, 1 inch will do, up against the roof, apply foam to these strips leaving a channel for venting. No matter how much you put in, it will be a great improvement.
This is my hunting camp, not a very complex structure. It is(was) heated with a kichen type range, 8-20 stove. It was unheatable on a cold night. We put 1 inch of blue styrofoam on the roof and shot shingles right on it. The walls are still not insulated. We had to let the stove go out. The floor is not insulated either.