In 2009 we drove from BC to Newfoundland, a great experience.
The ferries are huge ships, and we had no problems towing our 28 foot 5th wheel, total length 46 feet.
You have to make reservations on and off the island. We were told to make a return reservation when we booked the trip over, but we didnt do this as we hate being tied to a schedule and we didnt know how long we wanted to spend there. This worked out OK for us, after 2 weeks we called to make a return reservation and had to wait about 5 days for a vacancy but this was fine, gave us an extra 5 days there.
We got the "short" trip over to Port au Basques and drove all the way around to St. Johns area, then had the option of driving back over the same route (approx. 1000km) to Port au Basques or getting the "long" ferry trip from Argentia. This was much more expensive, from what I remember the short trip was about $350 and the long trip about $650, but we saved the cost of driving back.
The long ferry trip is overnight, about 14 hours. You cannot sleep in your camper so you have 3 options:
1. rent a cabin: 2. rent an aircraft-type reclining seat, or 3. use a regular seat. Because we made a last-minute reservation all the cabins were already taken so we took one of the aircraft type seat which was OK.
It all went very smoothly, but as we live on Vancouver Island we are used to getting on and off ferries.
I'm sure you will have a fabulous time.
2008 Ford F350 crew cab short box PSD, 2021 TravelAir 90W camper