The problem with waxoil is that unless you apply it in very hot weather it sets before it creeps into the seams, which is where the rust starts, I find that injecting oil into the hollow sections is as good as anything at keeping the rust at bay, it lays there and creeps giving continious protection. Waxoil or similar is better on exposed surfaces where the mud tends to dry and fall off, taking the lubricant with it.
Peter