If you want one of those puffers that bad go buy a 120 gallon tank. That's that. No if's, and's, or but's about it. Do it right. Ya know?
Otherwise think about it like this. Do you want to live in your closet? You'll fit in there right? Keep your food in there. Use the bathroom in there. Never leave. See how long it is before you get bored out of your mind, restless, and very sick. Very similar scenario as putting a fish in a tank too small for it.
Just think about it.
Valentini, Hawaiian Blue-Spotted, and Saddle-back puffers will all do fine in a smaller tank, but I understand. They just don't look the same... they don't really act the same either. If you like the look of the Dogface, maybe you can get lucky and find a Green Spotted Puffer. They are usually sold in freshwater but they do actually live most of their life in saltwater. You may need to start the fish in freshwater and gradually increase the salinity of the water over a few weeks. They are fun, similar physical appearance of a dogface, just neon green with black polka dots, and have a ton of personality. Best of all, they stay pretty small. 5 inches at most. A 30 gallon would be fine, a 55 gallon would be fantastic. Best of all you won't have to get rid of the animal after you've gotten attached to it because, TA-DAH! It won't outgrow the tank.
Hope that makes sense to you.