Bit the bullet last week and took the MP3 500 to France for a couple of days. Covered just under 1000 miles and no problems with the scoot.
Decided to go on the Eurotunnel. However when I tried booking online and entered my registration it insisted it was a small car, presumably because the Class 3 puts it in the same category as a regular trike or 3 wheeled car (Reliant Robin).
Phoned their booking line who agreed to charge me the same as a regular motorbike after looking up the MP3 online to check the size. They did say I may have to pay the difference on arrival if the staff at thd terminus decided it would take up more space but they were fine with it.
The only other issue I had was my 4 month old Garmin sat nav packing up while in France. Luckily I was back in Calais by then so finfing my way back to the Eurotunnel was easy.
I'm now hoping to make a return trip before the summer is over.