I also have a 30(ish) ft motorhome and tow a Sonic. I have towed it multiple times on short and longer trips, and all is good without a braking system. I do have one I bought off eBay for a song, and at some point may use it. I have tested it to make sure it does in fact work. I carry it in the "trunk" of the Sonic.
Be aware that some states require it for anything over 1,500 lbs, and some for anything. My personal opinion (FWIW) is that the MH braking and transmission are both up to the task of stopping both the MH and this very lightweight car. This is especially true with the Ford F53 with tow/haul (mine works great).
I also don't think you can stop a MH fast enough for the car to jack knife unless another vehicle or brick wall is involved, which brings in a different set of problems.