Walling your MCV is key, I do it in 100% of my QMs, if you do that you won't lose it and you don't have to worry about moving it which makes it so you can't build pillboxes, if they try to engi your war factory and you can't defend it, sell it and it's perfectly fine. You will have a better eco than them.
If you get lazy and they take one of your buildings (even your power) they could build pillboxes and spam barracks in your base and it will be hard to stop so it's always important to just sell any building they are going to capture it, especially when you don't have any tanks or ways to kill their pillbox spam.
Obviously you don't want to just sell any building they drive their engi flak / IFV by, but once it empties you could sell it and the infantry that comes out of it usually kills the engi