I slipped 2 x 4 boards under the tub, front and rear. They extended about 2 feet either side, so I could lift each corner a little at a time and block it up, working my way around until the tub was high enough to set the ends of the boards on saw-horses and then I rolled the chassis out from underneath....
I doubled the boards in the center and fastened them to the tub using the tub mounting holes....
Sorry no pictures...my real computer is in for repairs .....