Looked at the site. Am thinking they sand blast/or use some other kind of media. Then once all the rust is blown off, they build up with their 'molten galv metal. I pretty much use POR, either spray or can, for example the battery tray. But then again, I don't have spots the size of baseballs.
'90YJ Hard & Soft w/Full Drs; 4.2 Rebuild w/ Webber, 30x10.5; Interstate MegatronII D34; Mods: Rock Guards; Hi Lift Inst; Herc'd Tub, Front & Under; Elev Rear Seat; Scty CntrConsole/ Overhead&Rear Boxes; KC Lights-Fr & Rear; PA Sys; Gauges; Int Lts; Batt/Alt Cable; Heater Mods; 8K Winch, KargoMaster Rack w/Yak Megawarrior Basket; Ground Lights (4);Dumped - Optima Yellow after only 4yrs