Small pic, but it looks like your bunks are too short. My bunks guide me to the front roller.
As far as adding a 12" roller, a good boat dealer or trailer shop should be able to fix you up. Just measure the main frame channel width so they cam match it up. If they can't help, any decent welding shop can bend you some brackets to fit a 12" on your trailer.
California. Well it's like breakfast cereal. You get rid of the fruits and nuts and all that's left are the flakes. Thank goodness there's a place called Texas.
Stephen F Austin's Old 300
Sons of Confederate Veterans
Sons of The Republic of Texas