To answer your other question, standard size for rooftop vents/ fans/ aircon is 14x14". You'll want to brace that hole on four sides with wood, enough to get screws into.
Bruce, now you know how we get 200 page threads!
Jay, gas up before you get to 355. Figure two hours Rockford to 80 pulling the Roo-ster. Prolly heavy traffic near where 355 crosses 55, clear south of that. If you hit 80 later than 4:00 consider stopping for dinner. It won't cost you any time...