Good, modern window A/C are much more efficient than RV units. Less power consumed means a large units (more BTUs/cooling) for the same amount of current.
I have wonder the same thing as the OP and there are a couple of issues.
• Extending the controls from the front panel to inside. This might not be an issues any more because it seems like they all have remote control.
• Mounting the unit inside of a well insulated, waterproof housing
EDIT : I found one 5,000 BTU window unit that only require 11.5A to run (no start up spec). You could probably have TWO of them on an RV with a 30A power cord assuming they both do NOT start up at the same time.