74 power wagon dream truck...

First clean and scrub the heck out of it after it's been removed initially and when I say removed initially that means taking absolutely everything out of it and removing it... Very time consuming...
After it's out cleaned and scrubbed treating the inside of it... Then putting it back in and mocking up everything you plan to put in it... Take it back out fill in the holes that you don't want to use and resend the whole thing down in 100 grit then in 220.. clean it.. primary it... Paint it... And then start all over again putting it back in and putting it back together...