My recommendation is to do exactly what I did, find a frame in Central America where there is NO road salt. I swapped out the frame on my BJ60 2 1/2 years ago in Tegucigalpa, Honduras. Total cost INCLUDING parts and labor was under $1000.
I know of an RJ70 frame only a 1/2 mile from me here in Guatemala City.
this one is in reasonable shape... came out of Windsor, surface rust, potential issue with rear shock mount crossmember, front body mount cups need replaced. No title.
located in Davenport IA and $400 would own it sitting there. Apparently there are likely some Canadians that come down to Palmer Chiropractic College there, so there may be folks that go back and farth and might be able to haul for you.
let me know if youre interested and I'll PM you contact info for the owner
Got one under a BJ70 we are parting out. Canadian truck, body is thoroughly shot but frame is surprisingly not too bad for local rig. Definately would want to blast and POR 15 or something prior to use 15 min east of Abbotsford if you want to check it out... or email me and I can shoot some pics.
Can also get a RHD BJ71 frame out of Japan but shipping is silly on something that big.