Steelfist,
As mentioned in other posts there are many different kinds of battlefield damage and just as many ways to replicate it. Experience has shown me that you will definitely need to thin the plastic down from the backside of the fender to a avoid it looking like heated or melted plastic once you start adding the battle damage. Torpedochief did a nice job of describing some of the individual "tools" he uses to obtain different looks.

In my opinion nothing looks like dented metal more than dented metal, but replacing fenders with after market photo-etched versions can be very expensive and then end up being delicate and easy to rip off if you battle with your tank.

I'd like to throw out one other relatively cheap but effective way of adding damaged "real metal" fenders. This method works better on Tamiya tanks only because the fenders are molded separately, as with Hen Long the fenders are molded onto the hull. It's not impossible just a little more difficult to do on an HL tank.

I take the stock fender and using a Dremel tool I remove about the 1/3-1/2 of the lower portion. I make the cut an irregular scallop shaped cut to avoid having a straight hard line, which would be visible later in the project. Once you have the lower portion of the fender removed you can "re-sheet" the entire fender using thin gauged aluminum, brass or copper. You can find it at most craft stores, like Michael's and it only costs about $8-10 bucks for an entire role. It's referred to as tooling or embossing foil.

I used rubber cement to attach the aluminum sheet to the top portion of the fender. In this way I can maintain the stock mounting points for the fender ensuring proper location and a good strong joint. The scalloped cut helps hide the joint where the metal and aluminum overlap. Then you can bend or punch holes in the sheet metal for a realistic effect.

I've also included to pics of my Panther fender, which is still all stock plastic that was damaged using a Dremel bit, and heated slightly to add the dents and hole


I hope this helps, best of luck! Just remember to have fun and experiment.

Streetsquid