The Sprinter is a bit more complex to add a brake controller to. As the system is multiplexed the brake signal needs to be intercepted before the control module under the drivers seat. On our 06 even though the seven pin wiring was there from the factory it did not include a brake wire. Using internet resources I was able find a wiring schematic and then tie into the circuit before the multiplex controller. Some have simply added a second brake switch on the pedal linkage and used a standalone circuit.
You really need to research this for the newer model Sprinter and be aware that most likely the trailer will not interface with the Sprinter anti-loc system.
I would got to FORD and get a body builders handbook for your E series. Ford produces these to prevent up fitters, especially from the RV industry from doing things that will void the warranty and more importantly something that will affect safety. It is part of the FORD QVM program.
All the power tap points are there, shielding requirements, rear AC, body areas that you can cut etc. Great reference for all the chassis wiring as well.
If it is a "Wag Bag" system bag they are EPA approved for ordinary trash disposal. We use them whitewater rafting and have proven to be the best system for a small group. For larger groups we use a canister system that has to dumped in a sanitary system of some sort.
What Chassis? Our Sprinter chassis with ride-rite air bags would only allow the use of cable chains due to clearance restrictions. While I only needed them once the performance was fine. Of course drive slow....