I recommand
1. I stuff my interiors with Cotton Balls. They can be tucked into corners, pulled out loosley to cover more area. Do not try cramming them in there.
2. If windows are not in place put tape, paper whatever to block the windows openings.
3. Use Elmers glue to tack the doors on. This way you already have most of the openings covered.
4. Like Melgyver says paint before glueing (sp) together. Then touch up the seam.
Thought about masking the windows and glueing them in place, prior to your painting. That is what I did on my Hawk. Just a thought.
Hope this helps