[BB_TX]

There is no solution. You cannot exhaust air from the trailer without other outside air coming in from somewhere to replace it. Simply cannot be done. Otherwise you would be pulling a vacuum on the trailer. If the trailer were truly air tight, the exhaust fans would not exhaust any air.

Air can come in thru any small gap anywhere in the construction of the trailer. It can come in thru electrical outlets, light fixtures, around any plumbing entry point, around slide outs, and more.