cheers for the help guys.
my original idea was having 4 fans,2 for in-take & 2 exhaust fans. i was looking at some inline bathroom vent fans, their really cheap & quiet, but too powerful. u can get ducting that splits into 2, looks like a Y shape. would it be efficient enough to have 1 fan for intake of both boxes & 1 exhaust fan for both boxes, if i have the fans where the hole in my wall are?