You will have at least a 1 year warranty on everything on a new RV so you have that long to shop for an extended warranty. In any case, DO NOT buy a warranty from the dealer, you can do much better from third parties.
I second Ned's advice - don't buy through the dealer (they make a huge profit on those contracts) and don't rush into buying right any policy away. You can get "new" RV rates on an extended warranty anytime while your factory warranty is still in effect and you want time to shop around. You have enough on your plate taking delivery of a new rig, so save the warranty shopping for later.
If you decide to buy an extended warranty at all, definitely get a package for the whole rig rather than buying piecemeal coverage on appliances. The policies from the appliance manufacturers are expensive and it is much more cost effective to buy the whole package.
You want an exclusionary policy, one that lists the items that are NOT covered. If it's not listed, then it's covered. This type of policy will cost a bit more, but it's harder for the company to weasel out of paying. Get a specimen policy before purchase and read ALL the fine print. Make sure you understand your obligations under the policy and follow them rigorously. Any misstep can be grounds for denying a claim.
I would not buy a policy that restricts where the work can be done. There are a lot of choices out there so you don't have to be restricted in that way.