Better solution for fastening Dometic Sealand 711-M28 Tank to Floor?

[rich2468]

I replaced my recirculating Thetford Model 80 toilet a couple of years back with a Sealand 711-M28, but am finding that the 4 scrrews which fasten the tank to the floor have a tendency to back out of the floor on longer road trips.

The screws I used are the #14 x 2" long pan head screws included from Sealand with the toilet/ tank combo.

Realizing that the floor is only aluminum followed by light weight plywood covering a foam core and another layer of aluminum, I considered using longer bolts all the way through to the exterior with a reinforced plate on the outside, but the gray water tank is directly below the tank. So reinforcing from the outside doesn't seem possible.

I've considered trying to put rivnuts in the floor but I'm not sure that'd work.

Does anyone have any ideas of how to better anchor the toilet tank?

I don't have a photo, but here's a diagram for clarity.....