FromNH,
There are some here that will use the front seat for the child seat. I was never a fan of that, but that is an option. Remember, not only is your rig heavier than most other vehicles on the road, it's also quite a bit higher. So in a frontal collision with a passenger vehicle, all of the "action" will be at your feet level and below.
Just out of curiosity, why isn't the dinette an option? It it because you don't have one (table & chairs instead) or because there are no seatbelts installed at the dinette? Either is fixable, though the latter is easier and cheaper.
~Rick