welcome to the truck bike mafia, bro. make that thing your own! if you find something useful or fun to stick on there, just do it driving a cargo bike myself practically every day (a radwagon 4), i can highly recommend a bigger bell, and/or a good old ball horn. it's a huge quality of life and good vibes feature. both cut through traffic noise MUCH better and further than that flimsy little "ting", because of the deeper and louder sound. (and having to yell "WATCH OUT", if the bell doesnt work, is awkward and bad style) and an old school horn just makes folks smile, while instantly grabbing attention and politely alerting them of your desire to pass by. win/win! =) pro tip: attaching those gardening kneeling pads to the passenger seat(s) with self adhesive velcro makes them a LOT more comfortable and less slippery, for just a few bucks. your kids will thank me for this one. (i got a little cooler bag, a bluetooth speaker, a power converter and a deafening little truck horn on mine, plus ~10 gallons of saddle bags, due to the lack of a front bucket)
Install a flag on a front to increase your visibility. When riding near obstacles noone will expect your bike dimensions. Note that most bike trailers have a red flag installed.