Adding seat belts to a class A?

Although your ideas are great, their execution is where you run into problems. Securing the belts to the floor with large through bolts and large washers is about as good as it gets in that position. When seat belts first became available the Air Force Base I was stationed at required all cars be fitted with belts using that system. It worked but the difference in that system for your car and your idea in the RV is the structure of the seat. Car seats are MUCH stronger than the typical RV dinette. Just about all I've seen are made of 1/8" plywood with 1x1 soft pine structure held together by staples. In a crash the forward facing seat will collapse due to the downward force generated by the individual belted in. If the seat could be reinforced properly, it would go a long way to help. The rear facing part of the dinette would probably collapse and roll as the same flimsy structure broke up.

All that said, seat belts in the rear of an RV are simply there to make the buyer feel good, and as a selling point. There are no Federal Safety Standards for their use, installation or testing as there are for front seat belts and belts in other vehicles. Does this mean they are useless? I'd say no, but recognise what they are and why they are there. They probably serve to hold active children in position rather than allow them to be all over the RV. In a minor crash, they may well help to prevent injuries from being thrown about. msturtz's comments above are particularly relevant in large vehicle crashes, but seat belts in the rear of an RV in a catastrophic crash are at best problematical. Do what you need to do and what you think will be best for your family, but just understand what you are doing and don't think just installing a seat belt is giving you the protection currently available in other vehicles.

I was a licensed safety engineer and set up the child passenger safety program in Delaware before retirement.