You don't say precisely what model Caravan. This following publication is for the 208B G1000 Grand Caravan, and is dated 5th June 2008...
http://textron.vo.llnwd.net/o25/CES/...aravan_pim.pdf
On page 508 you'll find ..
LANDING GEAR
NOSE WHEEL TIRE PRESSURE:
30-42 psi on 22x8.00-8, 6-Ply Rated Tire.
MAIN WHEEL TIRE PRESSURE:
53-57 psi on 8.50-10, 8-Ply Rated Tires.
35-45 psi on 29x11.00-10, 10-Ply Rated Tires.