Do you plan to still open and close the garage door? For many years here in Floridawe haveinserted insulation or foamin the open slots of the frame and used cardboard andfoil tapeto hold it in. Home Depot sells garage door sealing strips for all four sides of the door, they work great. We use our garage for recording/band practice so the insulation/cardboard also works good for sound proofing...lol
We use a window unit, a couple fans and still use the garage door from time to time with no probs.