Best selling time for houses is the spring, so put it up this spring and if it sells right away, move into your RV in a park in town (or somewhere close) for the remainder of time before he retires.
Set up your SS for direct deposit. Never had a check come in the mail so that was never a problem. You are going to get a mail forwarding service right? Do that at least 3 months before you leave. If house sells, do it then.
Can he forgo vacation this summer and take it in January instead?
As everyone has said, take a deep breath, relax, and know that we have all been there, done that. We actually put our house up a year before we retired and ended up renting a duplex for the year (house sold in 3 days) for the year. So we downsized in two steps. Actually made it easier to do.
Barb