I've done Le Shuttle with a tandem. Relatively simple - you meet a guy in a hotel car park with a transit van and he loads you up and takes you over. The only downside is that it took a lot longer than we anticipated - with all the meeting and faffing it was nearly 5 hours.
I’ve done Harwich>Hook and found it pretty straightforward too.
Has anyone tried Le Shuttle yet?
https://www.eurotunnel.com/uk/travelling-with-us/vehicles/bicycles/