Ours came sealed as if someone was given a can of expanding foam and told "go!" so I'm not sure about the venting thing?I don't now what kind of "Critters" you are talking about but I keep field mice out of the trailer by laying laundry fabric softener sheets around the wheels (as well as on top of the wheels) and on the ground any where the F/W touches the ground...
The only thing about fox urine is you need to change it at least every week, the stuff that repels critters comes from the glands and its a small amount per...serving. You might have better luck than a friend did who tried that as well because his attracted BEARS. He didn't see any deer though, made for a bad hunting season.I'm on high critter patrol - after having them deposit food for the winter in our bed (seeds, pods, spider pods etc) and their waste in our bureau drawers on our clothing I have been sworn to prevent this from happening this fall. I have stuffed every nook and cranny with smelly dryer sheets and I've purchased "Fox Pee" which will go into small plastic containers which will be attached to the from FW legs. The Fox Pee was recommending by my son who was fighting mice for the last two years and when used this method it worked. We are also putting out small containers on either side of the garage doors since our garage was taken over by them while we were in Florida last year. I hadn't cleaned the deck on my riding tractor and they had a feast on the dead grass. When you live in the country you definitely battle creatures big and small.
Mouse-free works, simple as that. Spray it on once a year and you're good to go. Keeps crawling insects out, too.
John... Where do you buy mouse free?