1) Even if Lemon Laws apply, they always give the seller the option to repair it first...so it won't apply until you've gone back and for a few times (of course, the there is the question of if Lemon Laws even apply to RVs)
2) A lawyer at this point will just muck things up and cost you money. Again, they haven't said they won't honor the warranty. Unless the warranty has a time clause (it doesn't), they are well within meeting the warranty requirements. But if they start getting letters from lawyers, expect the dealer to lawyer up and stick to the letter of the contract and not the slightest bit more. Also expect them to try and turn it around as your fault.
Get an independent repair tech to get up on the roof, check the whole roof out and seal it up. That will at least stop any additional damage. The independent tech won't be covered by the warranty (you can ask but don't expect a yes for the warranty to cover him). This will secure your property and avoid back claims that additional damage was caused by your lack of addressing the issue.
Reality is warranties are not a good reason to buy a new RV.