So you are talking about #6351 the Porsche Jagdtiger that you must apply your own zimm ?
Most kit plastic fenders are one piece and usually a little out of scale,also you would need to cut up the sections.The metal might be the way to go for you,more flexibility.
Dragon also makes a newer Porsche version # 6493 which has the zimm molded on,its pretty nice but also has one piece fenders that have zimm but would still have to be cut if you wanted individual sections.I did do that one and it is a beautiful kit,it comes with MT's but they are tough to deal with,I used Fruils.Here is mine.
http://s180.photobucket.com/user/tojo72/media/Dragon%20Jagdtiger/DSC00128_zpsqrnrd1cc.jpg.html
Only the Porsche had zimm,hope this helps