Years ago when they were building stations, the equipment dealer that was doing the island would bring out a metal form, set it down and pour concrete. Not as simple as that but you get the idea.
This form would be used over and over. About two years ago, at an equipment dealer in Indiana, I pointed out the old form leaning against a fence, and he commented that he would give it away if anybody wanted it, otherwise it was going to the scrap yard.
Check with your local service station equipment dealer, he may have one you can borrow, or maybe to keep.
Jack Sim
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at
www.gaspumpbible.comAir Meter ID book also available