Most of us don't react well to change in life and a change in lifestyle is one of the hardest to make successfully. That's why many will try to adjust their lifestyle into RV mode while they're still working doing a "test run" of retirement mode. If that's not possible then the next best thing is to do a worst case analysis of your financial situation by charting out your actual expenses over the past couple of years. Assuming no change in spending habits this will give you a pretty good idea of what it costs to continue living the way you have been.
Other things to look at are which expenses will be reduced realistically and which ones will increase with the lifestyle change. Commuting expenses and work lunches for instance should go down if you're no longer driving to/from work and eating lunch out. But on the other side your mileage expenses will probably go up for the RV along with campsite fees, etc.
I switched to my expected retirement mode lifestyle about 10 years before retiring, paid off my mortgage and car loans, purchased and paid for my retirement toys (RV, etc) and tracked my actual expenses for those 10 years. When I got to retirement there wasn't much of a change that I had to make and I was pleasantly surprised to find that my actual expenses were running below what I'd been spending while still working.
Hope this helps, and good luck on your new career!