You can buy a switch like that at Home Depot. When you say size is no issue are you considering the mounting depth as well as the surface area? Most exterior walls are not deep enough for a standard electrical box so they have spacer rings to make up the depth, see example below:
Since most RV lighting circuits are fused at <10A, 12vDC does not present the same shock/fire hazard as household 120v, so RV light switches don't have to be mounted in the same insulating boxes as household switches.
You could always do something like this, same size as a residential switch but surface mounted. Click pic for link.
