If they are skinny chihuahuas, look at a "cat pet door" like this one:
https://www.amazon.com/Ideal-Pet-Pro...SIN=B0002805SM
Don't believe it would harm an RV door. My fat old Billy Bob, super chi can make it up and down the steps easily and he is old and fat. Your screen door will be the challenge. Perhaps remove the screen and put in a very thin piece of plexiglass; there is a small detent around the sides and bottom and make a hole similar in size to the pet door and figure out some way to fix a flap on the plexiglass. Top of the screen would still work.
Since we park at RV parks almost exclusively that don't like dogs running off leash, never really considered it.