I use a good rust cure ,its made by a company called granville ,sold in a little pot with an oil rig picture on it ,when we did will,s one (puss on here),his sunroof was the same as yours ,we hoovered out the loose then got a mini roller with the rust cure on and painted inside the roof and the bits we could not get to we used a squirty bottle with it in ,Yep would paint the inner wings and bulkhead aswell