Personally I have never thought there was much in it when choosing your vehicle type so I thought I'd have look today having just changed my number plate.
It won't have been updated on their (Brittany Ferries) site as yet (via DVLA) so thought I'd have a play.
Trip 14.06 - 21.06
2 Adults no extras
Existing Reg - Classified as Motorhome
Outbound - Afternoon Crossing - £155
Return - Night Crossing - £235
Existing Reg - Classified as 4x4
Outbound - Afternoon Crossing - £153
Return - Night Crossing - £233
A minor saving of £2.00 each way when classifying it as a Car/4x4
If I then start over and put my new reg in, it asks you to search. choose car/4x4, motorhome etc...
I then put Volkswagen (Make) California (Model) and then choose my options:
New Reg - Classified as Motorhome
Outbound - Afternoon Crossing - £170
Return - Night Crossing - £250
New Reg - Classified as 4x4
Outbound - Afternoon Crossing - £168
Return - Night Crossing - £248
Again, a minor saving of £2.00 each way when classifying it as a Car/4x4
BUT
Because my car isn't in their database they are wanting to charge me £15.00 more each way than a known Vehicle.
How bad is that!