For your 2005 Chrysler Town & Country roof rack factory bars you should seriously consider the Thule 604 Ascent 1600 cargo box (connects directly to the 2005 Chrysler Town & Country factory rack cross bars). The style & aesthetics of the Thule 604 Ascent cargo box match the Town & Country for a very nice look. Sounds like this gear box has ideal dimensions for your specifications too - 76"(L) x 33.1"(W) x 16.4"(H).
http://www.orsracksdirect.com/thule-604-ascent-1600-roof-box.html
There is also a very cool interactive tool for you to view this box, as well as others, on your Town & Country and see how it would look installed. Click here -
http://www.orsracksdirect.com/thule-cargo-roof-boxes.html and then click on the 'Thule roof box comparison tool and visual guide' link