Don't believe the dealer. Shop around, check RVServiceReviews.com for a mobile RV tech, and read up on the dealer's shop...that will tell you something about their integrity.
Expect to pay up to $300 for an extensive inspection, and make sure the purchase won't be completed until the inspection comes back good.
And 'Service Contract's aren't usually any better than promises by the salesman. Besides, that '99 is going to be too old to be covered by a service contract (only a manufacturer can offer an 'extended warranty' so don't fool yourself into thinking there is such a thing for a used RV). Take the money you'd spend on one...if there was one, and put it into the bank. Add to it each year. You've now become self insured and will save thousands. Most likely.