I made a L shape bench with two openings, one on each side. Now for the cover I used a piano hinge . I open it to change the litter boxes. I also put a rug on the top and place the bench close to my back window...
My cats don't like covered boxes. Have you used a covered one with your cats before?
They have dome covers. Gould have built the house around their needs.
See if these help! If they have their own space, I would build bench type enclosures.
Lucky kitties! My boxes are out in the garage.