The Proton Competition-run outfit joins the GTD division from this weekend's GT-only Lime Rock round onwards, with Cooper MacNeil and Jules Gounon sharing driving duties aboard the #79 Mercedes-AMG GT3 Evo.
It means the 15-car field for Lime Rock is now split between five GTD Pro cars and 10 pro-am GTD machines, with both classes using identical machinery.
WeatherTech originally lodged a full-season Pro entry with a Porsche 911 GT3 R while running an additional Mercedes, the #97 car, in the opening two rounds of the season, the Rolex 24 at Daytona and 12 Hours of Sebring.
However, from the third round at Long Beach, the Mercedes replaced the Porsche as the full-time #79 entry, with MacNeil having been partnered with a variety of teammates from the German marque's factory GT3 stable since.
Raffaele Marciello joined MacNeil for Long Beach before Daniel Juncadella took over at Laguna Seca.
Maro Engel and Mikael Grenier were MacNeil's teammates for the Sahlen's Six Hours of The Glen, with Juncadella being brought back for the most recent race at Canadian Tire Motorsports Park.
Now it's Gounon's turn to join MacNeil, the Frenchman having previously been part of the additional Mercedes entry at Daytona and Sebring.
“I’ve never raced at Lime Rock before, but I am looking forward to driving at this short and fast circuit,” Gounon said. “I will be looking to Cooper to give me some tips, then we can work together to get the pace out of the WeatherTech Racing Mercedes.
"On the sim I really like the flow of the circuit and especially the last downhill section.”
Just five cars now remain in the GTD Pro division for Lime Rock, with one car apiece for Corvette Racing (Corvette C8.R), Pfaff Motorsports (Porsche), Vasser-Sullivan (Lexus RC F GT3), Heart of Racing (Aston Martin Vantage GT3) and BMW Team RLL (BMW M4 GT3).
Vasser-Sullivan has yet to announce a teammate for Ben Barnicoat aboard its #14 entry with Jack Hawksworth still recovering from injury.
Kamui Kobayashi, who replaced Hawksworth at CTMP, will instead contest this weekend's Super Formula race at Fuji Speedway.