Does anyone know which software I can use to design mobile trailers and toilets with full detailing
The trailers also need to detail the 3D views and the furniture
Most any of the 3D design programs out would be good for trailer design. A lot depends on your experience level with such programs and how much you are willing to spend.
Free use, cloud based, and subscription service applications (Onshape, Fusion 360 and others) would be good for both a short term and permanent need.
Licence based software (SolidWorks, Creo, NX, and others) are a good long term/permanent solution and more expensive. You will always have access to your fills even if you do not keep a maintenance contract