The orientation of the hides may also help a bit. I have my snake in a 50g, which is too big but its all I got. I used to have his hides turned so I could see into them cuz I liked to look at him. He wouldn't go in them. Now I have them turned so his entrance is actually towards the back of the cage and he uses em all the time. He probably feels 10x more secure in them because he doesn't look out them into a giant room.

Also check the temp in the hides. Its wierd but the temp inside my warm hide is almost 3 degrees warmer than the area outside it. I'm sure there is a diff on the cool side as well, but since my snake is finally happy I just leave his habitat alone.