Seems like you would want snaps or straps, not a zipper. Have them sewed to the mat and case, using awl or heavy duty upholstery sewing machine, want it he!! stout for leather. Might look at duffle type bag that you could slip your guncase inside, or slip the mat inside the duffle bag. Go with a canvas or ducking cloth, similar to old sail material.... Or just take a 3' 2x4" and use some tent stakes to drove it down and then load up your bipod against it.
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