Belly Pan and tank woes...

We have taken a few trips this Summer so far. Having fun hitting the road. This last trip we were unable to find a dump station and travelled with a heavy black tank. By the time I got home the belly pan under it was sagging and the tank seemed to be sinking.
So now some repairs are in order. NOt sure exactly what I am going to do, but I think I will get the local fab shop to make up a pan, then put it in and add some support underneath. Looking for ideas.