Yes, there are several cases where windowless vans have been used in kidnappings for sex crimes.
I list a few examples below.
[Caution: The stories may be distressing.]
In 2013, the Ohio Attorney General warned parents of one or more suspects who were approaching children and had been unsuccessfully trying to entice them into a white van:
In each case, the suspect has approached girls and boys between the ages of nine and 15 while driving a white, windowless panel van, which could be a commercial vehicle. The driver has then encouraged the kids to talk with him and get into the van.
Fortunately these attempts were unsuccessful.
In 1989, a man was sentenced to prison for manufacturing child pornography:
Thoma lured the boy into his windowless van in the Back of the Yards neighborhood on Chicago`s South Side, where the boy lived, and offered him money to pose, Romza-Kutz said.
In 1979, the "Toolbox Killers" killed five southern Californian teenagers. Wikipedia explains:
Bittaker purchased a silver 1977 GMC cargo van in February 1979. The vehicle was windowless on the sides and had a large passenger-side sliding door. According to Bittaker, when viewing this sliding door, he realized he or Norris could "pull up [to a teenage girl] real close and not have to open the doors all the way." (Bittaker and Norris would nickname this van "Murder Mac".)
After unsuccessfully attempting to entice Schaefer into their van with alternate offers of marijuana and a lift home, Bittaker and Norris drove further ahead and parked alongside a driveway. Norris then exited the vehicle, opened the passenger-side sliding door and leaned into the van, with his head and shoulders obscured from view behind the door. When Lucinda Schaefer passed the van, Norris exchanged a few words with her before dragging her into the van and closing the door. Using a ruse they would repeat in most of their subsequent murders, Bittaker turned the radio up to full volume as Norris bound the victim's arms and legs and gagged her with duct tape
Similar techniques were used for their other victims.
[Wikipedia references a number of "true crime" books - I have been unable to confirm these passages.]