Wow, that is the mother of all inverters!
I am thrilled to hear that you got this used Tesla battery. I know there will be a lot of us here wondering: Can we get them? Does your guy sell to the public (or to your forum buddies? :B)
Your battery 'pen' looks great. I do have one concern. It looks like you have screwed the crosspieces into the cut edge of the plywood. That part of plywood will not hold screws -- they will come out. With the weight of the battery and the movement of the toyhauler, they will come out SOON after you get on the road. I can help you redesign it, if you need.