First, when you start the last chapter on Act Two, you will be driving the APC.
When you are driving keep going straight and you will see a clocktower, when you see it switch to the UV turret fast then start shooting the part where the clock is and you will see the kryll.
Shoot them fast (they come out from the clock part) and then hang a left, turn to drive fast, then switch to the UV turret fast then start shooting the kryll you might have lossed health for the APC. But if this tip is done correctly and you won't have lost any APC health.
Then keep on driving fast and switch to the UV turret fast when the old man yells "KRYLL!" and you are going to beat the level in no time.