This evening I installed a Progressive Industries EMS-HW30C in my 2016 x213. After checking with some other members on the forum, installing it right under the breaker box seemed like the best choice. I had an old dryer cord that I could use to attached the EMS to the breaker box so I did not have to cut the cord that came with the trailer (there is the extra unused red wire in the photos).
First step was to remove the breaker panel (8 screws) and remove the old cable (white, green and black wires).
Next, I pulled the original cable out, and then determined where we would be putting the box to make sure the wires did not get too messed up.
I attached the new cable (gray) to the EMS and the old cable (black).
NOTE: If you want the 136s delay on startup, take out the jumper now... Don't install everything and then remember, because you will have to remove the cover...

I taped my jumper to the EMS in case I wanted to find it again.
I then attached the gray cable (white, green and black wires) to the breaker box. While you are in there, give all the screws a turn... I actually had the ground wire to the trailer completely disconnected in there, so it would be a good thing to check.
I attached a piece of wood to the floor (well, the strips of wood that hold the paneling) that I attached the EMS to (not sure how thick the floor is, so I didn't want to screw in too deep).
I ran the wire for the display over to the access door on the right of the furnace. Not sure if I want the display flashing all the time (DW might not approve), but hiding the display in there so I can still check it seems like a reasonable plan (at least for now).
Hopefully this helps the next member, and thanks to all for the advice!
Edit: Don't know why the final picture is upside down.. seems fine on my computer.