this is just my opinion ......
but alot depends on the conditions of the workshop/garage / build area etc to whether you need to paint the chassis "as you build".....
I didn,t & found that cos my garage was nice & dry, no bad moisture / damp etc..... i found that my steel did not rust at all during the chassis making stage.
But i know that Dogwood & Ash built there chassis,s in a more open enviroment so had the need to protect the steel more than myself, so as said... depends on the build area conditions.
or how about using a dehumidifier in the garage during the chassis build??? would this help?
cheers
andy