I am using ESSTAC cards. There are many others out there as well as generics off amazon. Just get the appropriate side velcro from the hardware store and mount it up. As far as your finish goes I wouldn't even use the velcro. I would just buy a generic shotgun stock shell caddy and use it. They are generally made out of expandable fabric or neoprene and slip on over the stock. I like the Beartooth products ones.
The Velcro models are the best models. They weigh less and there is less chance of damaging the shotgun. The adhesive on the Velcro may damage the finish on your camo shotgun however.