Under arch protection

[HOT-ROD]

Not sure if this is in the right forum but I'm looking to get under the arches on the hotrod protected and painted. I need to do a bit of seam sealing under there and want to stonechip it. Now I've been told to prime it all first, then seam seal, stonechip and finally prime again and paint! Was advised against stonechipping straight onto the bare metal and told "It needed some protection first!" Is this true? Finally can anyone suggest anything that they've used that might be a better way to go?

Cheers