Try and find a car-jar battery with .125" positive plates and 5% antimony construction. This and glass mat separators are what makes up a "Deep Cycle" battery.
Interstate is a reseller. The only thing they manufacture is paperwork. Their production consists of warehousing and distribution. Some (not all) distributors (the people with warehouses and trucks) are well-informed about batteries. At Wal-Mart, the pimple-faced kid in the automotive department is about as battery smart as the teenager in Burger King who does the french fries.