Have you thought about a Fly-and-Drive? Find a good truck out in the dry side of the USA, Arizona, Nevada, California or the Eastern NW. Then fly out and drive it home.
Out here we have trucks as far back as the 60's that are rust free. I drive a 90 GMC that is completely rust free. To me it would be worth doing because you can fix anything, but rust is death to any vehicle. Starting with a completely rust free truck would give you a solid base, even if you need to fix a few small issues.
You can put a new engine in a truck for a fraction of what rust repair could cost you.
I know that the cost to fly and drive will impact the budget and may require you to spend less on the truck, but you will get a rust free truck.
You may not need to go all the way to the West Coast, but the supply of rust free trucks out here is huge, so there are a lot available.
Think of it as a foundation, you would not build a house on a crumbling foundation, don't build an Overland rig on a rusty foundation.