Obviously the plastic bottle stuff is best as pointed out above but I think I've read a post somewhere that does recommend against it.
If I recall, the main issue was water retention/drainage as you could prevent water from finding its way out of the drain holes. I used a light spray of carpet adhesive to ensure that the slightly undersized piece of insulation I used was held at the top so that a slight gap was left underneath. TBH I can't imagine the weight being a factor on its own but certainly if silent coating, sound proofing, insulating and carpeted ply panels are used then yes, the gas struts will struggle.