Many RV's come with King beds. The bed tops nothing but a sheet of plywood in most Rv's. That tops easily changed, I cut mine to queen for the added room around the bed.
Going from a 72" wide camper King to a 60" Queen is easy. However going the other direction requires a slide/bedroom build that accounts for the wider bed.
With our old 2005 Cardinal 29WBLX go could see the difference looking at the bedroom slide.
On our 2015 Bighorn the wide slide is standard and the mattress size is optional.
Our Rv had the optional king Bed from the factory. I have heard of people cutting their kings down to queens but have not heard anyone talk about going from a queen to a king.
So used to sleeping at home on a king, we made sure our new RV had one. Considered upsizing our last RV's bed to King but didn't want to lose the nightstands (and wanted a new coach anyway).
Queen at home. RV came w/ a King. Love the King tho a PITA to make, but I'll take the trade off. Stinkin dog still manages to lay crossways in the King, so your kinda reduced to just the same amt of room as we have on the queen. Grrrrrrrrr...........