He is Sharpei and Boxer - has a lot of the Sharpei traits (doesn't like cold floors, cold air and water). We've put his and his brothers bed in the garage and had them sleep there at night (insulated with carpeting on the floor) and then let them back in at night - he's good for a couple nights and then messes in the house again.

So are they in the garage all day and then in the house at night?
You could always try crating at night to see if this helps with the messes.

Is he getting enough exercise during the day, enough time out side to use the bathroom?

You can also try feeding him a little earlier and then having some extra time out side before bed.