Welcome Copasetic, they did come with a Gladiator owner's manual, I've archived it here:Gladiator Owner's Manualhttp://cpcparts.com
(Parkin Accessories) Is the company that currently owns all the remaining Gladiator/Glaval parts.
Take off the black plastic cover with a G on it, on the driver side of the 3rd row, it's held on with 4 screws and take a peek at the rear air unit for any leaks.
In the mean time, you should be able to stop it from leaking in the back by only using the heater in vent mode instead of heat mode. Vent mode shuts off flow to the back heater, but you can still have heat up front.