Starcraft 2: How to beat "The Evacuation" level on Brutal?

I have tried this mission a decent amount of times and I have been trying to build bunkers, fill marines up in those bunkers taht block the 2 entrances on the road but I cant seem to get enough marines to do so quick enough and then I don't have a big enough force to protect the transport vehicles. Is there advice, tips or a good efficient way to beat this level on brutal? I am struggling here and consulted some strategy sources but I am still failing lol