My son has 2 male GP, they live outdoors ( were outdoor pigs when we got them) currently in a 2 storey large hutch in a lean too with insulation etc to keep out the cold / draghts. They generally seem very contented, lots of happy squeaking, eat well, poops look ok, and they go in a run for hours every day for exercise / extra space etc.
Despite being outside GPs we spend lots of time with them, talking to them etc, but they aren't very tame 
Today I was cleaning them out and noticed that they have been chewing their hutch more than normal - their ramp is thinning hugely!
They are well fed, lots of toys / tubes and food sticks to chew / grind teeth on... am I missing something?