I worked in the Ford Transit plant at Southampton for 31 years retiring early at 55 ,21 years ago, all transits were subjected to a rigorous rust prevention regime,
The completed body including hood and all doors was taken through a special degreasing tunnel where they were sprayed at high pressure and temperature with demineralised water , paraffin and degreasing agents , the bodies were then passed through a continuous tunnel of demineralised water to rinse them they were then subjected to further sprays that contained Phosphate an anti rust agent, the bodies then passed through huge ovens and wind tunnels to completely dry them this system took an hour in total on an endless conveyor.
On exit from these tunnels the bodies were hooked up to electrodes for the next stage of their journeys, which was to hoist each body to overhead conveyors for their next stage which was total immersion into huge tanks of red oxide electrocoating liquid paint , they remained submerged totally in this paint which was very fluid bubbling and moving so that it entered every hole crevices joint etc including flooding the complete chassis of the build.
An electric current was then passed through the bodies causing the electrocoat paint to adhere to every surface, the bodies were then hoisted out of the tanks [ all automatically I add ] and they got another rinse on their travel to the next stage which was gas fired ovens to bake and seal the paint, This system was a bottle neck in the production because we could only process 25 bodies an hour but could build bodies quicker, hence this area was a big overtime earner working days and nights 7 days a week to keep the plant working .
The first part of the process being finished the bodies [a mixture of chassis cabs complete vans both large and small diesel and petrol on final build] traveled overhead to the next part of the process which was the sealer deck, on this deck all holes in the chassis had metal plugs inserted and sealed and all the welded seams [spot welded] were sealed with special sealant, wheel arches internally were sealed with very viscous sealant , black , the roof joints were sealed with another sealer from high pressure hoses [manually by operatives] as was the whole body.
The bodies then passed to the first paint booths , the priming sprayers, this was a manual spraying booth later to become automatic, the bodies all got 2 complete coats of primer paint inside and out,
We then transported the bodies through giant ovens to bake the primer-paint covering all done on automatic transport lines, after exiting the primer ovens the bodies passed off line to a holding area to cool as they were too hot to touch,
After cooling the bodies [computer selected for type, urgency ,and availability of parts needed engine gearboxes transmissions clutches etc ] for the further build requirements, went through what we called the sanding deck where they were sanded wet and dry by operatives following attached cards put on by our inspection guys on any snags runs etc they had detected , the bodies were then manually tack ragged, a sticky lint free cloth that cleaned off any dust left after the manual petrol wipe down and sanding process, the bodies then passed through a sealed compartment for high pressure blow off to remove any dust that was still on the bodies, after this they passed into the final paint booths for spraying with their final colour [ manual spraying later automated ] and also to receive any bake on floor coverings etc, before entering the final ovens to have the paint baked and finished.
Final painted bodies then went to the underseal area where the were undersealed wax oiled if that was on the spec and then got a final inspection and any defects in the paint was sorted at an off line facility called the 2 tone booths where they received any repairs to paint considered needed and also to receive second colours if they were ordered as 2 tone colours etc,.
Bodies then moved to the trim lines building for fitting out with everything a vehicle needs or had specified at ordering, We in later years started galvanizing the interior or doors and the interior of hood tops as these places due to extra handling by white van men caused paint damage and allowed corrosion to impact these areas.
So in my opinion Transit based vehicles got excellent anti corrosion treatment throughout ?
We often had visitor tours of the plant and the most commented on area of the tour by visitors was what we called the DIPPER TANKS where we submerged the bodies for treatment , people were amazed to watch this process.