Leonard Martin wrote:
"But how do I create a base for this thing?"

Best source of information is usually the supplier of the "thing". He
has incentive as it helps sales to show you, the customer, how to use
the product to your satisfaction. Telescoping fiberglass masts
especially need detailed instructions due to novelty and
complexity.Contact the manufacturer if the seller won`t help. He may
respond to an e-mail. They should show you how to make and place good
concrete.

Rohn Towers, for example, has published books on how to choose and use
their products.

The all-purpose source of antenna information, "The ARRL Antenna Book"
has in my 19th edition, tower bases on page 22-12. Unfortunately they
don`t tell you how to make good concrete. You need a mix rich in cement
(a 6-sack mix) and nearly as dry as you can mix it and be sure that it`s
just damp enough for all the cement to react sooner or later. You place
concrete, rather than pour it. It`s worth reading the book anyway.

Best regards, Richard Harrison, KB5WZI