There are no rear struts on a Stock Convertible Solstice, there is a Kit that you can buy to install one from the Opel GT version of the car sold in Europe. That costs around $120 USD's shipped. Or you can add some helper springs from Home Depot or Lowes for around $3.00 USD's If you PM mu I can send you links with the P/N's I Instructions.
I have the cheap added springs on my Convertible, but I do not car for the operation of them, with 2 installed it opens 2 fast & hard IMO, so I have ordered the Opel Kit, but have not received it yet.