Ah right, I thought you were talking about hanging a shotgun on the door lol
In that case I would still go with drill a 6mm hole and plug weld the bars in, but I would get bars that slip into the empty cases, then glue cases into them to look different
That's the idea of the 10mm bar. A .44 Mag case fits nicely over it.
Is it possible to plug weld vertically? Taking the door off is going to be a pain in the backside.