I think Nugget moved out of the house after his scare as his old burrow was back in use with tunnel holes being blocked off. But now he is back in the house again
So maybe the burrow is his safety contingency bunker
In case the roof ever comes off the house again. Must resist doing that. The idea of a lift off roof is good and I thought it may help with finding him for taming - but more important that he actually enjoys the house probably.