Welcome and congrats on the purchase.
Thor themselves does not offer an extended warranty. The dealer selling the RV will offer one, however, it may not be the best plan available. You can purchase an extended warranty after the purchase of the RV and sometimes it is best to take time, compare plans and then make a purchase decision.
If you discuss an extended warranty with the dealer ask about:
What is covered and more importantly what is not covered
Where to get service
How to file claims
Bottom line, do the homework before making a decision.
US Army (Ret)
2015 Thor Challenger 37ND
FMCA - F432054