looking good so far,
what damage do you want to depict?
as far as british or american AT weapons go, due to the marders light armour, and AT weapon would pretty much destroy it.
An anti-tank gun (including tank guns) would make a lot more mess of it than just ripping up the fenders.
A PIAT or Bazzoka would also cause severe damage to any part of the marder.
if the fenders are all you want to damage i would suggest a nearlby artillery or AT round esplosion, rather than a hit to the vehicle itself.
heres a pic of a destroyed marder 3H

thats the sort of damage an AT gun will do to a lightly armoured tank destorer
regards
joe