Look at the RV4
The RV4 has the seat belt anchors in the same position you do by design. A hole is cut low on the seat back just large enough for the buckle. This way the seat back is still easily removable. The other benefit is that your seat belts have a direct path from the anchors to you which is what you are going to want if, God forbid, you ever really need strength from your belts in an accident. The added benefit is no chafing of the belt material which will compromise strength.
Paid through 2018! How about you?