"slight" surface rust...depends if we talk the same language...but if its a slight , surface rust you can sand it or grind it off w a drill attachment w paint removal disc or sandblast it just get to bare metal w/o rust...if you have more rust you can after this use some 'rust converter', but I always feel better having the 'whole cancer' removed!
then after its gonme you can paint it just like the factory did OR you can go w POR-15 OR if you want to make sure, get the stuff they put in as bed liners in trucks ,"Rhino" but it wont be 'original', ...
If rust is all gone original spattter paint should do the trick..
Bjorn