I haven't spoken to the powder coater as I only noticed it had rusted this morning. I didn't ask for a warranty as I just expected it not to rust and, to be honest, it looked really good when it was first done. The grille was blasted and coated for £25 at a local place so at least I didn't spend too much. I think I'll sort it myself with Smoothrite when it gets too bad.
If I ever built another one of these I think I might just have everything metal - chassis, bulkhead, etc. galvanised during the build. Either that or move to Australia. No problems with rust down under, hey 1iTim