I'm in the Marine Corps - and trust me that your 12-13 weeks in boot camp will be mostly hurry up and wait. But if you do a lot of calisthenics (jumping jacks, push ups, stair climbers, etc.) you will be well prepared for the mental stresses of "IT" (Incentive Training). The longest run that you will do in boot camp is 3 miles - non stop - so your focus should be on 1/4 mile and 1/2 mile intervals for your speed work, 3 mile tempo runs, and maybe some 5-6 mile runs so that the 3 miles seems short. Running 3-4 times a week will be more than enough.
You're already ahead of the game if you're training now.
Semper Fi

If you'll be going to Quantico, you want to get used to hills.

Some good replys thanks guy, I think i should of mentioned that its the UK Royal Marines as opposed to the US Marine Core. Sorry I forgot to mention that as it does change a lot of the facotrs due to training difference etc. I have dually noted all the responses though, thanks and anymore help will be great!!!

I hear that Marines put cut glass in their socks--if they even use socks--or in their shoes just to make it a little tougher. (: Thanks for serving. Nick, Old Army.