I've found some aftermarket bumpers in American ebay. These seems to offer better protection than stock ones. They are unique to some small firm, which is making tough nylon bumpers for all popular RC's.
http://www.ebay.co.uk/itm/Ansmann-Ma...item1c1fd84538 (front bumper)
Also there is a front - rear bumper set for Macnum (but will fit the Rat):
http://www.ebay.co.uk/itm/Ansmann-Ma...item51992dfca7
And a nice wheely bar!
http://www.ebay.co.uk/itm/Ansmann-Ma...item519b5b5fc8
But prices are hefty.