Have you called your dealer? We have a 2019 331RL LOVE LOVE LOVE this rig.
Sorry I do not recall measurements.
We switched ours FROM a King TO a Queen. A lot of room lost having a King. In our opinion. Difficult to make the bed too.
We bought our Queen at a regular Mattress Store.
Spent a couple hundred bucks for the best and softest mattress ever.
No foam junk for us.
Hopefully someone here has your answer.