Probably the best kayak rack for carrying a single person kayak (but works with all types of kayaks too) on your 2004 Kia Sedona roof rack bars is the new
Thule 825 Port Side kayak rack. The 825 is red hot right now because it's both one of the least expensive kayak carriers available and it atteches to factory racks. But the best part is it carries a kayak semi-vertically in its j-cradles, which use up much less cross bar space and let you attach two of them to your Kia Sedona roof rack cross bars for hauling two kayaks.