Choosing to ignore your caustic remarks I will just address the reality of your 12-volt assertions. Few if any campers have 12-volt outlets available, certainly none that would support the current needed to power "appliances". Most only have a 12-volt plug next to the TV antenna which might power a 12-volt TV but only if it has the same dedicated plug which are a different size from standard 12-volt plugs.
I would be interested in seeing some links to all these wonderful 12-volt appliances you refer to. I have one of the 12-volt hair dryers that I bought years ago when I was ignorant about how things work. I still sits on a shelf in my garage and brings a chuckle when I notice it. Sorry, but the standard today is 120-volt appliances and equipment. Even if you can find a comparable 12-volt piece of equipment you will pay a premium for a mostly inferior product.
All campers already have 120-volt infrastructure in place which means, depending on how the inverter is connected, you have power available almost everywhere in the camper. Even though there are losses associated with inverter power they are nowhere near the 10 to 15 percent you state.
Post some links and proof of your assertions.