I tow a 2012 Smart Passion behind my 45 ft coach with no issues. I've towed it from Florida to Maine and back and from Florida to Alabama and back. It has a BluOx base plate and tow bar and hooks up and unhooks in minutes. I do not use an auxiliary braking system due to the weight of the Smart and I have a wireless tow light setup that plugs into my 7-way plug. I did have to install two round steel plates on the plastic roof for the light bar magnets, painted black and fastened with 3M double side tape.
I followed the instructions on the manual, I turn the key on all the way but do not start. Step on the brake and shift the selector into neutral, turn the key back to the accessory position and leave the selector in neutral. Ready to tow in 4 wheels down position. I do use two bungee cords attached from the seat frame to the steering wheel in a criss-cross pattern to prevent wheel shimmy and I've had no problems in over 5,000 miles of towing.
I love my Smart and drive it more than I do my pickup. It's awesome to zip around town or the RV park or wherever. I need it and it tows like a dream. I like to tell people I tow a full-size Smart Car with no problems.
I use an Ultragauge and have installed a cold air intake from SMart Madness. I also bought a scanner from Amazon and it works well.
FOXWELL NT510 Elite Scanner for Mercedes Benz/Sprinter/Smart Full System Bi-Directional OBD2 Code Reader Professional Automotive Diagnostic Scan Tool w/ HVAC ABS Bleed SRS TPMS Transmission Oil Reset. $179.99