Seen on the road in Canada a number of years back. Five identical bikes travelling two-up, with the last bike towing a boat.
As you can see, that tarp was mounded up pretty high - so some inquires were made.
The group was travelling Boston to Vancouver and back in two weeks. To save money and prevent time consuming breakdowns, the "trailer"
held the following:
Camping gear for 10 people
Large cooler with food and beverages
Spare front wheel with tire
Spare rear wheel with tire
and a complete spare engine (with all the necessary tools)
The rider said that it trailed just fine, and was OK pulling out - but a little squirrelly when stopping.