The one thing that i think would revolutionise the caravan is if some one were to come up with a fixed bed which could be folded /hinged, into the wall ,thus giving space during the day and folding down when needed at bed time . bedding could be designed to stay put during the folding up and down process.
Most fixed beds today are hinged to give acces to storage under the bed and to the water heater .the storage is not very practical and the water heater could be sited in the space aprox 400mmx500mm which would be formed at the bed head .
As part of your designe project,just think about it ,visit some caravan showrooms and look at the fixed beds ,then think with a bit of clever designe that bed could be hinged up and store aganst the back wall giving aprox 1.500mm x 1.100 daytime space . Good luck in your project Coljac