I would say that's too long for any dog to sit in a crate on a regular basis... maybe ok for an older dog (3+ years) on rare occasions. If 8 hours is a daily requirement, I'd find a dog-walker that can come in and give the dog a mid-day potty and stretch break. The biggest crate out there is 54", and Denna likes to stretch out more than she can in that one... and she's "only" 160lbs.
Also, being "crate trained" just means that they've been introduced to the idea and don't hate being in the crate. But, if it becomes a place where they know they'll be isolated and left alone, it could easily become a bad place in their mind. Be sure you reinforce the crate as a positive place... a 'den' for relaxing, napping and chewing on approved toys...