As a matter of fact, this month's issue of Aquarium Hobbyist magazine has a pull-out (aimed primarily at kids) that talks about 10 and 20 gallon fish only set-ups, using live sand and live rock. The clowns they advise are percula and ocellaris, (two of either) in the 10, and adding another fish to that in the 20. They also add hermit crabs and a starfish.
The article initially struck me as "no way," but think about it. LR
leave little room for cycling errors. . . not something you'd want a kid to fail on in his first marine attempt anyway. True clowns (percula) don't get very big, and still provide the eye-popping color a lot of people are drawn to marine tanks for in the first place. The article is very specific that other clown species are NOT suitable for either set-up, due to their ultimate size. With good husbandry, why wouldn't it work?
I'm thinking about the 20 for my office. . . .