One thing to keep in mind is if you do tilt the head, be careful when you tilt it, and when you raise it back up. Best is to have someone supporting the head while lowering, and pushing while raising. If you just try to do it 100% with the screw, you have a good chance of breaking it, and causing yourself a big headache.
I've moved several mills (2 series one and 1 series two), and each time left the head up. Two chains around the base (one around the base to the back, one around the knee screw to the front) will lock it in place. Then a few straps can't hurt. Make sure to lock the table/knee/quill. And go over the whole thing to look for loose parts that could fall off during transport (handles, covers, etc).
Here's my series 2 with my dad for scale. Rode about 2 hours home and didn't move an inch. The chains around the base were the main means of securing, the straps were more for my comfort. Had it loaded by a professional rigger who recommended this way of securing it.
And one on the ground, after unloading with my gantry crane. Took that really slow, but it handled it just fine.