I got approximately 1 year until I ship out for BCT. Any advice on how to prepare for it mentally and physically besides RSP?

You do not want to try and burn fat fast. Eat well balanced meals and gradually increase your exercise so that you are burning more calories than you take in. Do not put any food in your mouth before seeing how many calories it contains. Write down everything you eat and drink and the number of calories that it contains. Cut out all junk food. You will have challenges throughout life, so tackle them head on. Finish everything you start and do not quit. We all make mistakes, so learn from your mistakes and do not make the same mistake twice. Do your research to help you avoid making mistakes in the first place. Be a planner. Plan, set goals, and then accomplish them.

See a dietician, Diet is the number 1 contributor to obesity. Second, Cardio, not restricted to just running, but exercises targeting getting your heart rate higher, for an extended period. This will speed up your metabolism, thus burning calories at a faster rate then you take in. Bicycling, steps, ski machines all are low impact, high cardio, things you can do other then running - but, make no mistake, find time to run 3 x a week ( you will run a lot in the Army or Marines). Start with 2 miles, then gradually extend it as you improve. research videos on how to run, believe or not, the hardest thing is learning how to run correctly.

Start rucking. Get a rucksack (or backpack) and pack it to a minimum of 35 lbs. Start by rucking 2 miles, rest a week, ruck 4 miles, rest a week, 6 miles... and so on until you reach 12 miles. Basically, increase your distance by 2 miles every ruck, performing a ruck every other week. Your goal is to keep a 15 min mile. That will ensure that your final ruck, 12 miles, will be at or less than 3 hours. I saw plenty of guys get hurt, quit, fall out, etc. because of the rucking in OSUT. If you do the plan above, along with maintenence afterwards, it will help you immensely.