I tried to litterbox train mine for about a couple weeks, but recently gave up.
I'm probably not persistent enough, but he was pretty resistant to using them. When I would catch him getting ready to go, I'd put him in the box and he would use it, although he would never voluntarily get into the box himself.
Now that I'm outside training him, (crate training), things are going well and he rarely has an accident. I have him in a larger crate, and when I'm home I block half of it off and am careful to take him out regularly.
When I'm going to be out of the house for more than a couple hours, I take the divider out of the crate and put his litter box in. (I don't use litter, but rather line the bottom with a puppy pad). He always uses the litter box in his crate, and has never once soiled the crate outside of it.
I had really hoped the litter box would work ... I'm getting ready to move to Pennsylvania where the winters can be brutal, and was hoping to avoid shoveling snow each time he needs to go. However, in my case I think he's happier going outside, and the litter-box-in-the-crate and pottying outside hybrid system will work best for us.
I hope it works for you ... update me with your training system if it does!