If your coach has a steel or aluminum frame inside the wall structure, you might be able to find that frame, much like studs in a house wall, and hang your sink.
That said, I don't think even that framing has the strength you need for this mod. Even if you found a lighter sink, at least two factors work against you:
One, RV bounces down the road. This puts stresses on everything.
Two, You or somebody else may lean on that sink and find the mounting wasn't strong enough.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB