
Why not use the Harwich-hook of holland route and drive up to denmark?
It only takes about 6 hours and the ferry we have used had massive cage for the dog to travel in.
They did not allow dogs in cabins, only in the cages provided(not even in your car, as I believe a dog had been lost due to heatstroke).
We did do 28h ferry trip(Finland-germany) and they had a dog walking deck, so yes, it was outside they went to toilet.
But in this ferry dogs were allowed in the cabin and the cabin was very close to the dog deck so pleasant enough trip for all.