It's common practice in a multi-voltage environment to have all the electrical systems reference the metal structure. The 24 volt ac system used for thermostats controlling HVAC gear, the 120/240 volt used for small appliances, the 277 volt used for commercial and industrial lighting, 480 volt wye three phase used for larger commercial and industrial motors.. all have one pole semi-arbitrarily called "neutral" and connected to the building, the framework of the machines, etc. It's all tied together.
It's slightly confusing that in the dc world we call one pole "ground" instead of "neutral" but the principle of connecting one pole to the building (vehicle), machine chassis, etc still applies. You won't have any trouble caused by connecting the 24 volt solar's negative/ground, the 12 volt lights etc negative/ground, and the inverter/generator/shore power neutral all to the bus chassis. That's really the way it should be unless there's a clear reason to keep an electrical system fully isolated.