For a quickie setup, you are on the right track.
I don't know how much the tanks cost that you are looking at, but you might/should be able to find the 275 gal totes that are second hand. I find 'em in the local want ads. They usually go for around $75 - $100 each and are about 48" cubical.
The outlet spout is 2" dia, so no pressure restrictions. On the back of a truck, you will not be waiting long for 5 gals to drain.
If you want to take it up a notch, install a 12v Shurflo water pump inline with a switch and a few fittings. Hook it up to your truck battery.
