We have the same style window arrangement in our current hallmark and will have the same in our Alaskan. I asked if it could be larger, but the answer was no due to structural integrity. We have the donut foam cushion along with a round tube with stiffening on each end. Between the two the crawl space is pretty much w/o wind noise on the road and no problem for the dog to get through. I can crawl through in a pinch and it's handy to reach things in the rear seat, but definitely could be larger, oh well.