The Tank should get delivered to your hanger since it's too big to fit in a garage. The cargobob can lift cars on GTA: Online, but I have never tried to do it on Singleplayer.
It isn't in the hangar for some reason, but I've also had problems with the cargobob first. It was "invisible" and after switching between frogger and cargobob for 10 times or so it was visible on the H-platform.
I hope the lifting-thingie works in singleplayer. I don't know what I've bought the copter for elseway
it does work in single player, but takes awhile to get it to attached... (even when things seem to line up correctly)
I successfully picked up my tank with the cargobob so I could drop it off at the airport and have some fun!
unfortunately I found out the tank does not take a lot of damage before it explodes... especially if you run over a car and it explodes underneath it... insta death almost every time.