Just to go against the crowd, I always cook it and then freeze it in the tin. Defrost it and heat up on the day. I can't imagine why it'd go dry (good sausagemeat is so lovely and juicy and full of fat!!), unless perhaps you cooked it for hours the second time. So just don't do that
Thanks all. I ended up cooking it until it was hot in the middle but not properly done or crispy, then I cooled it and froze it. So will defrost and then finish it off in oven on the day. I hope that's an OK way to do it!