As previously stated, my first guess would be the evaporator condensor.

There are 2 other potential areas. You never mentioned if you have a
sunroof? Even though the '99 - '04 Odys didn't offer a factory
sunroof, many dealers were installing aftermarket units. If you have
one, the drain tubes could be clogged there as well.

The other area that comes to mind is the windshield. Here again, if
you had one recently replaced and it wasn't properly installed this
would most definitely be a trouble spot.

Since you don't mention if you are the orignal owner, a windshield
could have replaced before you purchased the van. So you may want to
have it checked?

Good luck