I was able to use acrylic to support the Prusa PCB heated bed for printing PLA (bed below 70C) but not for printing ABS (bed above 100C). I think wood (MDF) is commonly used to support the Prusa heated bed with some spacer like cork. Others mount the PCB with standoffs on the Y-plate and put either aluminum or glass plate on top of it.
If you use an aluminum plate with wirewound power resistors for a heat bed, then it supports itself.