I have an F250 with a long box so I don't have trouble with fit, but I back my Griz in and can put the back tires up against the front of the box withought worrying about the window. I also put a piece of 3/4 inch plywood in to keep the box from bending.

 

i'm not sure what kind of truck you have but when i went to pick my grizzly up at the dealer when i first bought it, the guy who works there rode it up it to the truck and he forgot to put the parking brake all the way in, after about 15 miles of of hauling my griz home, about a quarter mile from my house the grizzly roled ahead and smashed the back window out.
My dad went ahead and put a fiber glass window [img]i/expressions/face-icon-small-happy.gif[/img]