Travel to Europe via UK by car

You can’t stay in the car during either trip. If going on a large ferry from Dub to Holyhead then you can book a cabin. For England-France, consider the tunnel if you’d prefer to stay in your car as that is how that works!

you can book the 2 crossings as a package over the phone through stena or irish ferries and the package is called "landbridge" and has its own price matrix, just look at the website. Simply explained, its cheaper on weekdays (mon-thurs) than weekends, and the ferry from UK to FRA leads to a cheaper price than the tunnel, but the difference in summer isnt massive and the tunnel is way quicker.

When calling its wise to have the times of the ferry / tunnel crossing to hand that you are looking for. They also ask for all passenger details, incl dates of birth.

One thing which is not explained to any extent by any ferry company for brand new ferry customers, is that "check-in" with a car is not as you might imagine it. Its not a case of getting out of your car and going to a desk in a building to a uniformed member of staff..... like I did on my first ferry crossing from Cherbourg!
No... its just a checkpoint with a hut at the entrance to the port, like a toll motorway toll booth, and they give you any document or boarding pass you need.
Eurotunnel is the same, but speedier in all aspects.

On a ferry, you can stay outside the whole time if you want but a cabin normally doesnt cost much on the irish sea crossings. It can be booked over the phone along with the landbridge deal.

I'd say that the reason you can't get a cabin on the ferry is because the truck drivers are being given individual cabins instead of sharing with strangers.

The ferries will have to implement social distancing so even indoors you will be fine, if someone gets too close just go for a walk on deck and then sit somewhere else.