I am trying to buy an inexpensive Samurai  ( before 1990) this/next week. Everything I can find in my area is quite rusted out.... No "big deal" as I have some experience in body work - but since I want to do it right I am planning to sandblast the frame, re weld if necessary and then rust proof. I have heard good thing of POR 15 but this will still not solve the problem on the inside of the frame. What can be done to truly rust prove the frame - I was thinking of hot galvanizing - but the question there is if the frame is strong enough and doesn't get twisted because of the high temperature involved? Has anybody hot galvanized his Samurai frame??

That would be crazy to hot dip a frame, all the holes would be plugged
with the galvanizing metal. You could do what they do for aircraft and
get a creeping rust proofer, it's designed for spaces that can not be
accessed, spray it in and it covers the metal preventing corrosion

Wild

Crazy bad or crazy awesome?

  Has anybody hot galvanized his Samurai frame??

Some (~25) years ago I had some parts flame-sprayed with Zinc. It left a grainy porous surface, a bit like sandpaper. Should hold paint nicely.   

Hot dip galvanizing the frame should be fine.  Check with the place you'll use and see how they want it prepped.  I'm involved with some land rover groups and galvanizing is something very common in that circle.  Just have to plug up any threaded holes or you'll have to run a tap through each one afterward.  Most galvanizing places charge by the pound.  If you're bringing your frame you might as well bring whatever else you can from the truck that will rust.

Almost every replacement rover frame is galvanized:
http://www.roversnorth.com/store/m-131-richards-chassis.aspx

Also, I wouldn't recommend painting the galvanized chassis afterward.  The paint never seems to last (but the galvanizing will). 

Another option is something like waxoyl:
http://www.roversnorth.com/store/m-19-waxoyl.aspx
You can spray it inside the chassis rails and on the outside.  There are two different types depending on where it is being applied.