I have the GTS smoked covers on my 91. They should fit your 88 perfectly.
The model # is GT0147S. The "*" at the end, means "smoked". You can also get them in "clear".
I paid $88 Cdn for them, and had them ordered from a local performance shop.
BTW GTS'* website is http://www.gtstyling.com
PS- I don't believe they make covers for the tail lights. The tail lights on an SSE model "almost" looked blacked out. Or you can follow the instructions found in the "tech info" articles. http://www.bonnevilleclub.com/techinfo/?article=20