Our rig is a 2007 model year with tires dated spring of 2007. Like you, we keep our rig indoors away from sunlight but I have no plan anytime soon to replace the tires. Given your rig is a 2551, it is on the lighter side of motor homes so there is less tire pressure and less weight on the tires so the demand on them is less. I would think you would be fine getting one more year from them and evaluate again one year from next spring.
Regarding batteries, assumed no winter camping plans, I would charge them and bring them into your house out from the extreme cold. The same for the chassis battery. Fill your main fuel tank up, blow out all water lines, drain all four water tanks, place numerous rodent traps around inside and abandon the rig until preparing for your first trip next year.
Next spring, I plan to replace our 5 year old 12V Walmart batteries with 6V Duracell batteries from Sam's Club. I did some measuring and determined that my slide out battery tray will need to be replaced with a simple sheet of steel to get adequate clearance because the 6V batteries are so much taller. The sheet steel will have angle iron screwed to it to cradle the batteries so they don't move around on the large surface.
Thanks for the tips. My Pole barn doesn't get below freezing and always kept mh there and never had any problems with the batteries. I would like to get another year on the tires.