I would say the AVERAGE is $30,000/yr. Some stay at fancier 'resorts' and take in a lot of entertainment. They would require more.
Some don't move or move 2x/year and don't do much as far as entertainment. They could do it on $15,000/yr.
Some travel almost constantly but take on volunteer gigs occasionally for 3m at a time which gives them a free campsite. Entertainment for them would be mainly enjoying nature. They could do it on $20,000+ because of traveling constantly. This is where we fit in. However, we did pay cash for our two RVs and vehicles during our 16 years of full-timing so you have to take that into account.
Years ago we spent a lot less than 15 years later. All prices for everything increased.
You are young and didn't state when you plan of leaving the workforce. You will have to take into account inflation, how you plan on full-timing, will your present 5th wheel and truck still be serviceable when you plan to start.
Good luck in your plans.