Before I give it a try and before I mess something up, has anyone removed their back seat bottom cushion (only)? Any tricks or hints? When the folding seat backs go down are they 'flat'? Do I need to place something under the folding seat backs to support them? Currently my seat backs when down are not flat and are angled. This is not good for my old Retriever in her crate for our six hour ride to our cabin.