You didn't say if you are experienced in RVing so that you know what it entails.
If you are presently an RVer and are sure you want to full-time, I would get the RV, list the house and work on the enormous task of getting rid of everything. If the house sells fast then you're good to go.
If you need the money from the house sale to buy the RV then you'll go the opposite way.
It's done both ways depending on your circumstances. It's a great lifestyle. Good luck!