Originally Posted by J Mac
A roof mount will have a controller in the trailer where as a portable has one mounted to the back unless you order one without. You have to decide if you want to bypass the controller on the portable and use the one in the trailer, or if you want to use both of them. There's a post somewhere on the forum where the member had an intermittent issue where the voltage from one controller tricked the 2nd controller into thinking the battery was already fully charged when in fact it wasn't.
If you bypassed the portable's controller and hooked directly to the panel input on the trailers controller this would not be an issue, as long as the controller could handle the additional load.