Don't do it!
Unless your life's partner (How was that for inoffensive?) is willing to commit to your dream and make it her own, it's never going to work out for you. I tried this with my wife of 30 years. She soon became my ex-wife.
Sounds like you folks might benefit from taking a crewed charter for a week or two to shake out the sea legs and determine if mal de mer is going to be a problem for your wife. Don't invest in a new boat until you get this deal breaker figured out.
If you determine that the ocean's going to remain a dream and not become a reality, gas up the RV and get moving! There is no end to the beautiful places you can discover while driving around the back roads of North America.