Problem is the sheet could lift and you then deposit quite a few gallons of water on the floor and through te ceiling.
If you can get your hand under the bath,get a piece of 6mm plywood, drill a hole for a 6mm bolt , bolt length about 35 mm. chamfer off the edges of the ply and dril hole in centre, now apply a generous amount of silicone sealant, fit over hole, now fit a penny washer over hole in ply and again seal with silicone,insert domed headed bolt, and under the bath atach another piece of 6mm ply, apply a generous coating of silicone, now put on another penny washer, and the nut, tighten and you woill see th esilicone ouzing out around the joints, smear flat, leave to cure for a day.
Fill bath up with water,and mark water level with you in it, and keep an eye out for as drop in water level.
But it should hold,beware of catching yourself on the domed headed bolt.