In Cab Leg Strengthening
The warm up routine for the FIT system includes a squat. This is done while standing between the seats in the basic athletic position. That is feet shoulder width apart and about 60% of your weight on the balls of your feet. Then squat down until your butt hits your bed, then lift back up again and repeat. It is important to do it the way the book tells you.
As a runner I have come up with 3 more resistance exercises that you can do in your cab. The first one is a simple calf raise. You can use the FIT system for this. A calf raise is simple. You can do it with no resistance other than your own body weight. Start in the basic athletic position. Lift your heels off the ground, as if you were going to stand on your tip toes, but you are really standing on the balls of your feet. You can add resistance with your bands attached to the floor mounts. Lift them up your sides to the point of resistance then do as you did before. The tubes increase is resistance as they stretch. You can also lift them shoulder high and do the same thing.
The most common knee injuries in running are called Runner’s knee (this feels like someone is tapping your knee cap with a ball peen hammer as you run), and illitopial band syndrome (that feels like 
someone is sticking a needle in the side of your knee while you run). They are unpleasant. They are also easily preventable. Both of them have basically the same cause. They are a slight dislocation or tilting of the knee cap. They usually happen when a runner is increasing their distances too fast. The kneecap is held in place largely with your quad.
You can strengthen your quad by doing leg lifts. Buy yourself some ankle weights. Sit on the edge of your bed with the weights attached to your ankle. Do 1 leg at a time. Lift the leg almost until your knee locks and the slowly lower your leg back down. After you are done with your leg lifts you will want to do some leg curls. Leg curls will strengthen your hamstrings to balance out your quads. These can also be done with your ankle weights. Lay on your stomach. Curl your legs up towards your butt. Then lower them slowly until your knee gets close, but not reaching the lock or straight position.
These are important exercises if you are considering running. Don’t even consider running until you can walk. Work yourself up to where you can walk at a brisk pace before you start including ANY running into your routine. Doing that and some lifting will help prevent injury, and that should be the main goal of your resistance training.