Get chain for the rear, put your rig exactly where you want it then put your chains exactly how you want them. Straps for the front and tighten it down. Also if you have a winch use it to secure the front so it doesn't bounce. Always and I mean always have a safety chain on the front, it doesn't need to be tight but if your rig breaks loose of the straps you won't loose the thing off the back, plus it is required by law to have a safety chain. Now when you unload your rig undo the front and backup until you can free the rear chain and leave the chain hooked to the trailer that way when you reload your rig you just re-hook the chain and then drive forward till the chain tightens then just strap down the front. Also don't just get any old hardware type chain make sure to get towtruck/flatbed truck rated chain and that goes for the straps too.
Here's a good source for this type of equipment, don't go cheap or you may regret it later:
http://www.awdirect.com/
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