I see trailers/boats behind FW's all the time on I65 in Alabama and I75 in Georgia. They are either coming from on going to Florida. It must not be enforced much in those three states. I saw a large utility trailer with two Harley's on it a couple of years back behind a 30' travel trailer (not FW) on a US highway in central Alabama. I wish I knew how long this rig was.
My FW moves vertically so much at the rear when I travel over uneven roads I couldn't feel comfortable with a trailer back there legal or not. I wouldn't put a bicycle back there either. I have seen too many bicycles bouncing around in front of me on other trailers that I was sure would fall off any minute.
I just don't need this concern when traveling.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof