Sorry to hear of your loss...
I had stuff taken from an M35A2 at Anneville also - batteries and box, alternator and bracket, compressor, power and start switch. Filing a claim was a waste of time. I ended up having H&S Towing pick the truck up off base for me.
DO NOT assume that GL will hold the truck for you. Call Amanda at the Mechanicsburg site and/or Mike who goes up to handle the pick ups at Anneville and make sure they know you are still picking it up. I just had someone at Mechanicsburg mark 2 items I won worth $550 as abandoned - even though I had arranged to pick up said items this week. I just filed a claim on them and was told it would be a minimum of 15 business days for them to figure out they screwed up. While I wait, they have my money.
I'm not sure if it's a scam, incompetence or just miscommunication on GL's part.
CALL THEM!