Went there last week:
There are a lot of trains in and out of there:
If you go there, be sure to eat at The Packing House, right across the street:
On a side note, there are a bunch of Mauser, Gustloff and Walther trainer rifles in the basement part. He's reportedly doing a book, so they aren't for sale.....yet. I was able to go down there. Some are marked with NSKK, NSFK etc. Looks like a lot of work will go into the book, so can't wait to get one if and when it comes out.
I don't think you specifically need an invitation to go to the Luger Room. I just asked and was escorted in there along with the basement tour.