Does the interior smell stale, or just the seats? Identifying the source of the offending odor is the key. If it is the seats, then a thorough cleaning could be the answer. I like the Blue Coral product BB mentioned above, though I generally use that for headliners and spot cleaning upholstery. For cleaning entire upholstered interiors I'll use a product from a local janitorial supply created for use with upholstery, it is more economical and easier.
If after you've cleaned the seats it still doesn't pass the smell test, borrow some of the wife's Febreeze and give that a shot.
krtoflas, wouldn't you clean the material before "sealing"?