Growing Leylandii in large container

[garjobo79]

I'm on a mission. To hide behind trees. Fast growers, to be able to keep out of the nosey neighbours glare. So space limited. Would love to know your thoughts on these types of trees. Yep, they are not friendly to others but grow quick and leafy. I plan to plant them in a box, a good 1 metre by 2 metre depth a metre too. I know they will grow..ok...thinking 8foot be happy with. Thoughts. And best way tk prepare..holes in side of wooden box. A mixture of manure...what do they like....I would also be digging up from garden a couple which are a good 8foot...so....thoughts on making sure they survive? As usual welcome any advise.