I agree about contacting manufacturers. I'm not sure there's anything unique about a captain's seat or bucket seat, since regular autos have a variety of seat types. So having a quality seatbelt to secure a good quality carseat should be fine. The table, most likely, is removable or collapsible, so a child wouldn't hit against it anyway. Those bench seats should have seatbelt down behind the cushion - fish around and you'll find them! Our rentals had seatbelts in the couch, the bench seats, and the one bucket chair we had on just one vehicle.
I think you're ticked off at your husband, which is understandable if he bought a big-ticket item without your involvement. But that's a separate issue than child safety, especially because there is no child here yet. Approach both of them separately. Certainly, a big investment that didn't allow for a child is a problem, but I'm not sure that's the situation here.
We rented an RV on 3 separate occasions for vacations, and I have to say that we had a remarkable time. We enjoyed traveling with all the comforts of home (well, in a compact space!), and we really enjoyed going from place to place without having to unpack and move into a new motel with each stop. We found the friendliest people at campgrounds, and got a lot of help from staff as well as very experienced camping families if some little thing went wrong that we didn't know how to fix. Our son enjoyed playing with other kids, running around the wooded areas, fishing in the pond, and every other low-tech form of entertainment, you name it. He has developed into an independent and confident man who works well with so many kinds of people and who isn't dependent on luxurious surroundings, video games or other technology to have fun. I attribute this to a lot of things, but his experience in traveling with us and meeting new people is high on the list.
And all of those kids traveled safely in a wide variety of RVs and campers.