Never done that, but here a the reasons I would say a second controller is in order.
First off you want to be able to set the response of the trailer brakes to match the weight of the trailer. Highly unlikely they will match the tag axle.
Second I would question that the 2 controllers are even of the same operating type.
Third there are times when you want to be able to control the trailer brakes without having the brakes on the tow vehicle come on. Sway control and wet road conditions.
Considering the weight of the MH and that most brake controllers are inertial activated or some form of none operating timer I would recommend a Jordan mechanical controller. It is the only controller that is directly connected to the barke system and thus operates as a function of the MH brakes. The problem is someone bought Jordan a few years back and they may no longer be available as new. I would look for a used one. Some modifications may be necessary to install it but it is worth the effort if stopping the trailer is a consideration.
Yes you will have to manually wire in the new system. Considering the length of the MH I would go at least 1 size larger on all wiring and make the brake signal to the trailer 2 sizes larger. This will reduce voltage drop over the length of the MH.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles