What you do is remove the lower section of your AC unit so that you can look up in to the bottom of your system to see how the duct is sealed. Then you get a roll of aluminum duct tape and some latex duct sealing paste at Home Depot. After you have cleaned everything and resealed the ducts, then you cover all of your tape joints with the duct sealing paste. This will prevent the tape from coming loose in the future.
While you are at it, you will find four bolts that secure your AC unit to the coach. It is a good idea to check them to see that they are SNUG, not tight, which will ensure that your gasket is compressed enough to prevent water leaks.