I've taken the Roadster on the Supercat service to Jersey a couple of times - before the MulFab sump was fitted.
The crew were really good, they knew what the car is and as it has a fly off handbrake they always strap Mogs down, not just chock them.
I had no issues with the ferry ramp, but exiting in Jersey at low tide the car grounded as I drove off the ramp, which is why I had the MulFab sump fitted.
We will take the Plus 8 next year, it has better ground clearance than the Roadster.