Thanks for clearing up the crate size.
What is in the crate with him currently? blankets, toys, a bed, newspaper, etc?
Does he totally not care if he is covered in his own pee and poop?
I would try getting an ex-pen like this
Black Exercise Pens- With Walk-Thru Door and putting a bed, the petapotty, a pee pad, some toys, and a water bottle in it. See if he'll choose either the petapotty or pee pad to potty on instead of just going anywhere.
ETA: Personally I do not like the idea of getting a big crate and putting a pee pad in there. A crate is suppose to be den like and dogs do not (should not) potty in their den.