Take measurement from the center line struts to the outside of the gussets going of the outside of the frame. I think you will see that the struts in question are mainly supports for the center line between the sheets of plywood for the original floor. Moving a few inches should not be a problem a far as frame structure. You may want to lay the sheet of wood that covers that area across the frame rather than along the frame.
If one of the seams, of that sheet, falls in an area that will see human traffic, not just under cabinets, you can glue and screw a 6 in.strip of ply to the underside of the sheet at the edge and glue and screw the next sheet to it. This will support the seam between the plys. Just be careful that you are not directly over the tank and screw into it. if glueing and screwing a strip are not an option there are what are called "H" clips made of sheet metal designed to support seams between plys. maybe a better idea through out the flooring.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles