When we had a stray dog for a few weeks, we tried the "doggy litter" stuff and hated that the pellets were so big. So I can not suggest a litter box with that stuff in it.
Most people here I think use the litter box with a pad or cat litter in it. At least I think that is what I understand. The stray dog did learn to use the litter box very quickly, but the big (now wet) pellets could not be easily separated from the dry pellets and we ended up putting a pad at the bottom because urine would still collect in the pan.
I think a box for the pad, be it a litter box or a refrigerator pan, is a good idea because they will not accidentally walk off and do business thinking they are on the pad. Penny does this several times a day because her pad is just on an office chair pad. (We are going to train her to a Pet Loo in a couple of weeks.)