Directly under the DT I reinforced each beam with another 2x12 (both glued and lags). Under those on each end of the DT, I stacked two 4X4 (making a 4x8) which I lagged together). Under those I have floor jacks each capable of holing 20,000 lbs. (2 total). One of these walls is also under the tank giving additional support. (I believe in over engineering ;o) I'll add a couple pictures later.