I had an inquiry a couple weeks ago asking about how to keep snow from blowing in during the MN winters. My suggestion was (Although I didn't use it because my daughter thought it would look s-t-u-p-i-d... This is foam pipe insulation sold at Lowes or Home Depot in lengths of about 6 ft. It's alredy slotted to slip over a pipe, so you can just snap it over the hatch door edges and help close some of that extra space.
I'm not certain that it is durable enough to last more than one season, or to stay in place when traveling, but it's cheap enough that replacing it wouldn't be painful.
Happy Trails! Jeff