Can't help there, except to say there's got to be a tradeoff between concealment and accessibility, as usual. Seems to me the fastening strong enough to prevent the gun from falling out on top of you if you hit a goodly bump would inhibit the ease of fetching it when needed.
One of my Audis had a "ski tunnel" in the trunk which ran under the back seat. I could keep a rifle in there, but if I ever had to get it in a hurry, forget it. The concealment was great, but the fetchment sucked.
Terry, 230RN