The big issue here is safety vs. legality. Legally, you are probably fine wherever your kid is sitting. However, safety-wise, I wouldn't put a rear facing seat on a side facing gaucho for any more than an around town trip. Obviously, you can make your own choice, but you want something that will hold the seat securely to the gaucho if you are in a front end crash.
Also, side-impact protection on car seats assumes that the seat is strapped into a forward facing seat in a car and the car is then hit from the side. There is basically no testing for a side facing seating position in a van/rv.