"He was a hard-working man who was a paint sprayer by trade and he had a really happy life.
"Our son was a wonderful man. He was kind and gentle and that showed with how many friends he had.
"Everyone who knew him will miss him so much and we cannot believe that he has gone. His mother and I will now start to grieve for him, but it will be so difficult as he meant the world to us."
Mr McCaffrey's van, which was left a wreck after the crash, is being looked at by forensic experts. Police are gathering statements from other drivers who saw the lump of rock being thrown from the footbridge across the A41 close to Rock Park.
Meanwhile, Wirral South MP Ben Chapman has called for Wirral Council to act to protect motorists.
"I will begin lobbying again for either high walls or a cage around the bridge to protect motorists from such a deadly game."