Aluminum stock trailers with 2'' air gap above fenders

[AC Diesel]

I'm looking at buying a new aluminum stock trailer, and it has the 2'' air gap down the side above the fender wells. You can close the gap with plexiglass in the winter.
I'm just curious if anybody has this option and what their thoughts are of the gap. I'm seeing a few of them on the road but not many. I'd post a picture but I'm still computer illiterate, it's a Barrett trailer and there are some pictures on their website.
Thank's in advance AC

 

[Big Muddy rancher]

I have a new Duralite but it doesn't have that air gap but it has 2 six inch ones at the top with track for plexiglass. I had some Puck board that I used as I think it is tougher then Plexiglas.