Good information here as we are debating the same situation.
Tow dolly about $2000 or 4 down about $4000.
The 4 down is wired brakes on the car, blue ox.
But if we change cars we have about $1500 or more into a toad we have to do again.
Not a fan of the brake boxes.
We will most likely go 4 down, and just plan on keeping the toad.
But alas, we also must make a decision before May.
Thanks again for all who replied to the thread long before I got here, great ifo from both Dolly and 4 down.