On the official website they have a special ticket for vehicles with weight more than 30 tonnes: https://www.adony.hu/kozlekedes/ So while it's not easy, it should be possible to cross here with a big camper van. 

It's a double lane ferry, so even oversized cars should fit. I never crossed here personally, but used other similar small ferries in Hungary, and I've seen trucks crossing on them This size is quite common here, I cross on this one frequently and they use a similar boat with a very similar pontoon: https://www.openstreetmap.org/way/40268134

I can add an hgv=discouraged and trailer=discouraged. 
https://wiki.openstreetmap.org/wiki/Key:access#access-discouraged
https://wiki.openstreetmap.org/wiki/Key:trailer

On most route planner you can set to avoid ferries. 