I've been using waxoyl professionally for 20 years http://www.peterflynnclassiccars.com , it works. If you were to buy a Independant Fabrication steel bike, they do it as a matter of course (waxoyl like product). I can't understand why the cheaper frame manufacturers Brant and Cy come on here saying it's a waste of time. It costs next to bugger all, is easy to clean up with white spirit – what's the problem, if you bought a steel frame with your hard earned money, surely you'd want to preserve it, for a few quid. I did my steel frame from new – that's all you really need, once from new then forget it. If you still own it in ten years, why not give it another application. I think Singular apply a cavity wax or frame saver too before sending the frame out, IRC.
Clear Waxoyl from halfrauds or similar, in an aresol (if you haven't a compressor) job done!
I have welded a steel frame that was rusted, before – it had no Waxoyl in it! I also repair lots of classic cars with it in the box sections, it just requires a little more effort in cleaning/prep.