Strap the bike to the D-Rings on the bed floor. If you haven't added D-Rings to the front of the bed, do so. Search the forum for how to add them. You're better off adding them to the bed-frame bolts than you are drilling into the side of the bed as Toyota's directions that come with the extra D-Rings tells you to do. Never strap your bike to the plastic cleats in your track system.
From my experience recently, if i made it through 4000 miles of cross country driving using the stock plastic cleats and the rear d-rings securing my motorcycle you should be ok. The weight on my motorcycle is around 425+lbs. In your situation, your dirt bike should weight alot less than a motorcycle. For the front, I strapped each side handle with 2 cleats (so i used all 4 cleats for the front) and the rear 1 d-rings on each side of the motorcycle as shown on picture. Although on each rest stop, i always check for tightness always-both cleats and straps. Good heavy duty straps is highly recommended. My straps are recommended 1000lbs per. Good Luck!