I moved the batteries on out TT last year from the tongue to underneath the TT under the kitchen where the power center is located. I was planning to mount the batteries inside the cabinet under the sink, but I was concerned about the safety and lost storage space. I ended up making a frame for 2 agm batteries out of steel angle from an old bed frame and mounted it underneath the floor between the frame of the TT and the skirting. I did this to power an inverter which I mounted under the sink. I did the wiring just as you described and simply removed the battery leads at the tongue. I left the disconnect switch in place on the tongue to turn off power to the jack when needed, and placed a new breaker/disconnect at the new location. My plan is to install a mesh floor to the underside of tongue to store wheel chocks and leveling blocks.