Over five years ago we put this pair of GC2 6V batteries into our 2005 25 ft's battery box. Width and length are perfect, but battery height was over an inch excessive. No problem, formed C-channel as height extensions for battery box.
Because of good battery management by my solar controller and Intellipower converter/charger, this 5.5 year old pair of batteries test nearly perfect. No measurable swelling, great charge cycles still. BTW, we top off at four or five weeks the cells with distilled water. Also keep cells evenly filled, clean and free of any contamination by using a filling manifold. I think there are pictures in my forums gallery. If not I'll add a couple to show this.
The switch to GC2 batteries has been just right for us. Glad they fit our battery box so well, approx 3/4" overall margin on N side, half that on E and W because of the 3/8" tie down bolt.