A law suit will not get your RV repaired, at least not for months or years.
You do have the right to take the vehicle any place you'd like for the repairs, or at the very least have an independent appraisal done. You need some kind of ammunition if you're going to dispute what you're being offered and I've not seen any in what you've posted so far.
Finding additional damage once the repairs are started is not unusual and in the case of significant damage should probably be expected.
In a perfect world your insurance company would send someone qualified to appraise the damage and completely explain that appraisal to you and what you can expect moving forward. Fact is, most insurance companies don't have anyone on staff qualified to do a damage appraisal on an RV.
Jay & Peggy Monroe with Dolly
Can't take it with you - don't plan on leaving any behind
2016 Newmar London Aire 4553, Spartan chassis
Wrangler Unlimited toad