I purchased a Grey hound plastic carrier from Petsmart, it was the largest they sell. I drilled 4 holes into the side of the carrier, 2 holes for water bowls, 2 for perches. It takes the entire space inside my car and the rear seating. It works perfect, it keeps my GW safe, large enough so my GW does not feel closed in and he enjoys being inside of it as he knows we are taking a trip somewhere and my boy loves to travel.
The upper side of the carrier have many holes and cut outs so there is plenty of air flow. It has a very large door so it's easy to place the GW inside and to remove him. i have to figure out how to post more pictures of him so you can judge for yourself on his size. I know he is just over 1700 grams. Best of luck Joe