If its for the one you had off me mate dont bother unless you are gonna get it sand blasted and properly painted or powder coated, believe me i have been there and done it with the hammerite and the finished product is pants. There is a chap round the corner from me who does powder coating said about £15 – £20 to do but would have to put in with another order to make it worthwhile needs it back to bear metal tho.
Personally I wouldnt bother, if you wanted to get it blasted i would happily take it to him for you but i am sure there is someone more local to you, steel fabricators ususlly know someone, honestly dont go down the hammerite route you will regret it mate