I checked with Bennington and center support on trailer and lift are required with SPS. I didn't ask about Express Tube, but I did specifically ask about SPS. Required. Too much weight for the frame to support in the middle without support.
I'm not sure where Bennington has this documented, but I was shopping for lifts, and the lift dealer wanted to put me on a lift that lifted the boat by the frame and leave the pontoons unsupported. I said 'no' and he went to the 2 bunk lift. I said 'no'. He said it would be fine. I said 'no', he said he'd call Bennington. He called Bennington and came back with "ok...3 bunks it is..."