What is this crank for?

It is for the wife to use on the manual mixer, when making margaritas.

The dealer must have put in in the RV by mistake.

Powered tongue jack emergency crank

Ultra Fab 3502 manual crank, and is inserted under plastic plug on top of jack.

The Ultra Fab "Ultra 3002" electric tongue jack on my toyhauler uses a handle exactly like that.

Looks like the one that came with my electric tongue jack. Sorry, I don't remember the brand. Utra Fab maybe.

Maybe for manual cranking of slide room?

The Barker 3500 on the trailer uses a square tube handle. I can't remember what what out last tongue jack handle looked like, bu it was also a Barker and I think we gave the new owner the handle for it.

I had one that looked just like that, it was for the electric tongue jack. Hope this helps.