It will be pretty stressful for him - any chance of having a really responsible person take care of him at home instead? If not, then just make sure he's got everything he needs when you go. Don't feed him just before leaving and do give him a chance to use the box then, and show him the new one as soon as you get where you're going (any chance he could have his own small one for the duration?) as well as a safe room to 'land' in - the new smells alone will be enough of a surprise, never mind other animals - or are there any there? Are the people at the place 'cat' oriented in that there won't be any dangerous hiding places he can get into (apart from under furniture) or things that he could pull down on his head, etc.? Will they be scrupulous about not letting him run out if a door opens?