This is what I would put on my Mossberg 500 or Remington 870 if I had one. http://www.blackhawk.com/product/spe...k,1156,165.htm
It's not a soft grip but you could do any number of things to make it soft. The Knoxx stocks are supposed to help with recoil as it is but if thats not enough put a limbsaver grip or something on the PG. Get creative.