Hi BT... Nope I don't think chrome would be a good idea for the mufflers...What I do is paint them a dark brown color first I use humbrols 98 chocolate color...I then grind up alot of different brown and black pastels and while the paint is still wet I use an old paint brush and cover it with the different colored pastels .This gives you the rough rusty look . If the pastels don,t adhere anymore just add a bit more paint to where you want the pastels to stick and and more .I use the black around the hole to show exhaust staining.. try it ...it works and it's fun... Here's an example of how it looks.
http://www.nutsnbits.com/rcraig/S010.jpg

Rick