We had a Siberian Dwarf hamster who did fine in the normal habitrail tubes. He was an adult when we got him, second-hand. He wasn't much of a digger - the most digging he did was to immediately empty his food dish and bury the food every time. He was more of an "up" hamster - he would climb on his branch just to jump off the highest point, and best of all was climbing up the habitrail tube, stopping at the top, then pulling in all four feet as close as he could so he just dropped, really fast! Are your dwarf hamsters adults, or still babies?