In Washington, vehicles that are older than 25 years are exempt from emission testing. You don't need to have "Special" plates, just the age. You mileage may vary. Check with your local licensing agency.
On topic, I wouldn't shy from a vehicle just because it has a carb. Yes, there are many advantages to FI but a conversion would cost well over $1,000 which takes a huge improvement in MPG to make the investment worthwhile. Especially given how few miles most RVs are driven. As a previous poster stated, there are many specialty places that work exclusively on carbs and can make an old one like new if needed.