how to prepare photo for garage wall?

I have a client who would like several large (20x30) photos hung on a garage wall.

In the midwest, humidity is a problem and this garage is not tight or air conditioned.
I hope to avoid a 'print' that ends up with wrinkles/waves.

I am open to any method. Dry mount, canvas, under glass, etc.

any ideas?

What about a metal or acrylic print? No issues with warping or wrinkling.

I've gotten metal prints from adoramapix and have been happy- haven't tried acrylic yet.

I considered metal, but not acrylic.....

any other ideas?

Have you considered flush mounting on masonite?

I was in an exhibit a few years back and had a diptych in that exhibit that was two 32 X 54 inch horizontal prints that were flush mounted on 1/4 inch masonite and were place one over the other with 12 inches between the two.

I would think your best bet would be Metal, Canvas or Acrylic. Mounting on masonite might work but with humidity it's not recommended. You can also mount canvas to masonite that would be better -- but again masonite is very heavy and pretty expensive compared to the other alternatives I mentioned at the the top. I grew up in Iowa I know the humidity quite well!. ha.

Here's a great site thru which to order metal (aluminum) prints:
http://fineartamerica.​com/metal-prints.html

A commercial client of mine recently ordered a slew of 36" by 24" and 48" by 32" metal prints from them, and they came out looking great. FAA really does a great job with these aluminum prints.

Terrible website for the prints. Can't find the cost unless you upload images and create an account. Or at least not intuitive enough to find cost in a reasonable time. Of course I assume if you have to ask...