Have the tire store check with Michelin about whether your tires are on recall.
I had some tires that I thought weren't eligible for recall but Allen tire store determined that they were eligible. Six Michelin tires for your rig should cost around $1800 total. Tires that have sidewall cracks are prone to come apart from pounding on concrete pavement on hot days. If existing tires have original rubber valve stems, "bite the bullet" and have long solid metal custom formed valve stems installed.(Tire Man or Borg or Camping World) They make checking air pressure much easier with beauty disks on wheels. Don't use cheap screw-on "extenders". They are prone to leak and can lead to tire failure from running soft. Tires and brakes are crucial to safety of RV's. Have brake fluid replaced if it has not been done in the last two years. It absorbs water and can cause brake fade on long grades. Have entire brake system checked and serviced as needed. Have engine cooling system checked and serviced as needed.
Have house batteries load tested and check whether the converter/charger is charging them when rig is plugged into "shore power" Should read 13.6 volts at battery terminals when rig has been plugged into shore power for 24 hours.
Batteries last about 10 years if kept charged properly and electrolyte levels are maintained with distilled water.