I think Jayco's come with at least a one, possibly two year manufacturers warranty that should cover everything. They will make more money on these extra/extended warranties being offered than they will selling you the RV. If the overall quality of the rig and its appliances make you think you need an extended warranty you are buying the wrong rig to begin with.
Keep in mind that warranties, both original and the extended add ons are only as good as the dealer who may or may not stand behind them. Unless they are close by with an established track record for quality after sales service I would not put much stock, much less money in that direction. Chances are you will be a long way from the factory. A thorough PDI of a quality unit is your best bet.
As always.... Opinions and YMMV. :C