Not sure about the Sportrak but my '93 Fourtrak TDX had a genuine Daihatsu tonneau cover fitted. It was a grey PVC coated material secured with press studs along the edges above the rear folding seats and loops that fitted onto the rear headrest pillars. It even had securing tags fitted to the rear seat just in case you needed to roll it up, only one I have ever seen.Obviously unlike a parcel tray it could not carry any weight but kept what was in the rear area private. Might have been an optional extra on the Sportrak?