I go mudding all of the time... and I have never had to worry about any mud getting into the zippers of my bags... The flaps (they velcro down) cover the zipper portion... and keep all of the mud out...

good luck with your choice... let us know what you go with...

 

I have an American Trails zipperless that I really do like. It is amazing how it can keep the dust out and store so much. Found it at Sportsmans Warehouse for 129.00

 

I've had nothing but good luck with the Mad Dog bags I have bought. My fender bags have zippers and get dunked in mud and filth on a daily basis and I've yet to have any trouble with them. The best part about the fender bags I have is that they're so quick to get into. With them you pull the velcro flap, yank down the linked zipper and you're in. No messing with buckles or straps just a quick two motions and you're in.

I'm going to pick up a pair of their large rear rack bags before the rifle deer season. Quality stuff at a reasonable price..

 

I hope this isn't another one of those posts where everyone submits an idea and the person that asked the question never comes back and tells us what they decided to go with...