This is testing my memory from 1982 Army Reserve days, but my experience was that when the hood was laced shut on wet days, there was a bad problem with exhaust fumes entering the cabin.
By experimenting, I found that by rolling the side flaps up, the exhaust did not reach the driver. Rolling the rear up made the problem worse.
It could probably be made to work as well, if the front ventilators were opened to pressurise the whole cabin, but on a freezing day with rain, that idea did not appeal to me,
Cheers Charlie