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There are a number of smaller sized tours of similar nature. Companies like Trek America and Suntrek have young adult oriented tours using 15 passenger vans (maybe 12 guests and driver), some camping, some hotels. Companies like Intrepid also run van tours across the USA and Canada, though they are not 100% young adult targeted, so can draw a wider age range.
The party atmosphere really depends on who is in the group. We run into these companies frequently in the western USA, Canada and Alaska. Some groups hoot and holler all night long, some groups are quite sedate enjoying glass of wine, not a keg of beer. The companies all market the "have fun with other young adults" aspect emphasizing the nightlife, fun and games. But they draw a wider spectrum of travelers.
One aspect to consider is time of year, shoulder season (spring and fall) dates seem to have a wider age range in the groups, whereas summer trips seem to be predominantly college kids on summer break.