I replaced my batteries after owning my 2015 30T for 8 months. The service garage, put in cheap batteries which eventually lost all charging power 6 months later. I put in Interstate Batteries and I have not had any problems since. Also, I had to replace the battery in my '06 Honda Pilot. I used Interstate again. Like the warranty and they have locations across the USA.
My $.02: I would recommend AGM type from any reputable manufacturer. Cheaper batteries are not always cheaper in the long run. Be sure to keep the new batteries charged and don't discharge them below 50% state of charge, or below 12 volts, measured with a reasonably accurate volt meter.
On a 1999 vintage consider upgrading the charger/converter as those are famous for boiling the batteries to death. The Progressive Dynamics with the Charge Wizard have a true float mode and will also desulfate the batteries automatically.
2001 Winnebago Adventurer WFG35U