I use those exact lights, here's my setup:
1.) I spliced into the dolly light wiring, and attached a plug where the magnetic lights can plug in.
2.) I put a receiver on the TOAD, main purpose to be able to easily move the dolly around if I needed/wanted to, or when not towing to handle a bike rack. I bought a piece of angle iron at home depot, think it's 4' long. With some threaded rod, permanently clamped it to a standard 2" receiver and ball, which is slid into the toad. (The angle iron runs parallel to the bumper).
3.) The magnetic lights sit in the |_ of the angle iron, as I didn't want to risk scratching the car finish. I had painted the angle black to match the receiver. The wiring runs thru the trunk and car and out one of the front doors, to connect into the plug as described in #1.
I leave the wiring in the car and actually tucked it under the carpet and door jams as it runs thru the car. The lights when not used, are just unattached from the angle iron and placed in the trunk. The front connector just lays under the front floor mat.
If I need to move the car dolly around any significant distance, just attach the dolly to the toad ball, and move it wherever.
The hitch with angle iron attachment, is easily removed from the toad with a pull of the receiver pin.
Works very efficiently, and can hook it up in a couple mins. Probably don't really need the magnetic lights, but they were cheap enough and easy enough to add on I figured I'd just give it a try.
DaveB, Raleigh, NC
2015 Tiffin RED 33AA, w/Honda CRV
VMSpc, Magnum BMK/ARC50