Did America have any POW Camps in the continental US during the Second World War (besides Japanese Internment Camps)? If so, what were conditions like? What did prisoners think of them? Are there any surviving diary entries or interviews from former inmates?

Yes. The United States housed several hundred thousand POWs in the US during the war, which I've written about here. Happy to help with any follow-ups you might have, and I'd also highly recommend We Were Each Other's Prisoners by Lewis H. Carlson, which I mentioned in one of the follow-ups, as it is an oral history collection which includes over 100 accounts from both sides about the POW experience.