You are on thin ice here comfortable is a human emotional term, applying it to a snake is very iffy. Do my snakes eat regularly, thermoregulate and display relaxed normal behaviour, yes they do. Do the ones in a rack do this yes, so do the ones in a tank and custom enclosure, there are the accepted markers if the snake is secure in its surroundings, comfortable if you wish to misuse the term. I believe that there is ample evidence that a tank can easily produce health well adjusted snakes for long period of time. If fact I can say longer lived than in tubs, many times, the 3 longest lived Royal pythons (at least 47 years, the oldest) were kept in a display enclosures and certainly not in tubs. Perhaps in twenty something years this will be challenged but currently there is no records of long lived royals in tubs (yet anyway).