For any multi-layer part that has significant rust and scale between, you will normally see the tell-tale signs of swelling between the two parts, especially noted in the middle between spot welds. Yours still looks flat, so anything between is minimal at best. I'd media blast in the crevices for a good abrading for paint to stick, followed by a quality epoxy primer. But prior to spraying, use a brush with your epoxy primer and attempt to brush and "wick" the paint between the panels in an attempt to fill any void. Wipe off any excess and spray away.
If you do see any signs of significant rust, you could always remove the part by drilling out spot welds, clean all parts/fabricate new as needed and reassemble using plug welds.
