FromNH,
Welcome to the forums.
When our kids were small enough to use car seats, we dropped the dinette table (into sleeping position) and put the car seats on the back bench facing forward. Our belts adjusted fine, but if yours are long you could probably wrap the extra around something to take up the slack, or just replace them with shorter belts.
We also were able to put them on either of our two couches facing forward by resting the back of the car seat against the rear arm rest of the sofa, and then creatively running the seatbelt through the back of the child seat.
All of that said, and without starting another forum discussion about how one type of RV is "safer" than another, I view seatbelts in a motorhome the same as seatbelts in an airplane. They are there to keep your butt in place for normal bumps and evasive maneuvers and, should we be unlucky enough to require them, minor to medium impact collisions. Should we be involved in a collision so severe that the very structure of the motorhome fails, than I don't think seatbelts are going to make much difference when a 300 lb. refrigerator and 50 pound microwave are coming at us at 50+ mph.
Also remember, in your motorhome, you are statistically in one of the largest and heaviest vehicles on the road. In a collision, mass is your friend. Put another way, I've always felt our kids are safer in our 22,000 lb. motorhome than in our 4,500 lb. minivan.
Drive defensively, make sure your vehicle is operating within it's specified chassis limits (proper tire pressure, weight limits, etc.) and enjoy the trip! :)
Safe travels,
~Rick