When I first took my M3W on the Eurotunnel in 2015 I asked them if it was considered a motorcycle. Despite my best efforts they insisted it was a car and had to have a car ticket.
At some point since then their rules appear to have changed and this year Martin Yates queried them again and has got confirmation from their Customer Support Department that Morgan Three Wheelers now are classed under motorcycles which is significantly cheaper. Following this two Mogs (a Super3 and a M3W) have booked as Motorcycle/Trike and travelled without problem.
To book, do not enter your Reg number but instead select “Make and Model”.
Then where it asks if you are travelling with a Motorcycle select type & Size.
Select Motorcycle
You will see the question “Is it a Trike? Select yes and this takes you to the booking page😊