Germany to Denmark route options

flatcoat

we will be travelling from Plonersee (near Lubeck) to Holbaek Fjord in a couple of weeks. There are two route options, road (long way)  or road and ferry (shorter). My guess is the journey time will be similar and although the ferry option saves about 100miles I suspect the ferry fare of car, Caravan, passengers will cost more than the fuel saved. Has anyone travelled both routes with a Caravan to advise?