American made tires will do you good, personally not a fan of Firestone but American made & 10 ply you should be good to go!
On another note “6 year old tires” should be replaced or short, light load trips recommended with heavy monitoring of tire pressure and look for age cracks (Dry rot) in the sidewalls.
RV Tires are absolutely not an area you want to gamble with. My top 3 priorities:
2- Tow Vehicle
3- Weight Distribution/Anti-Sway hitch
Ron & Debbie Smith
2020 Kodiak Ultimate 2922FKDS
2016 GMC Denali 2500 Duramax
Proud USMC Combat Veteran