Most people don´t know but its possible to use a rock besides the sandbags to pass them.
So i´d prefer to say: Mine the doors @ Valley although it might be painful with only 12 mines.
Also i wanna let you know my prefered HON mining. Defendet Walls or Eyes HON in some 2h+ games like that. I´m sure some don´t like it, i´d still strongly recommand it.