i am a painter for a living 8 years exp
if you want a bullet proof finish
heres what you do going with your plan
2 coats of the kilz on the framework is great
after you get the skin on do one coat of stain let dry for a day then do 1 coat of Varathane Diamond Water-Based Polyurethane with a good brush sand with 220 grit then do 1 more coat
http://www.rustoleum.com/CBGProduct.asp?pid=70
you can buy this stuff at home depot or rona
and if you want even more i would caulk all the joins and seams on the inside with alex plus and do one more coat on the inside
if you have any more ? shoot me a pm
and also when the paint soaks in to the wood than is a good thing