The brush arbor services were and are generally very fundamentalist. A lot of the more bizarre religious practices, from snake handling and speaking in tongues, to being "slain by the Lord", took(and take) place in these services. The services in slave times may have actually often celebrated the "old religion", in which celebrants were possessed by various of the spirit, often with a Christian veneer, like Voodoo. As you come from a more progressive religious tradition, you might want to differentiate yourself in some way, so people know what to expect.

Also very interesting(if a bit more mainstream) were the old Camp Meetings--In the summer, they met in a sort of tent city in a pleasant, scenic, rural setting--there was a main tent(for the revival services), usually in the center, and it was surrounded with smaller tents where the participants stayed. With the passage of time, the main tents were replaced with pavillions, and the smaller tents were replaced with small houses. These small summer towns usually could be identified because they had the word "Grove" as part of the name, like Ocean Grove,NJ Willow Grove,NJ and Pitman Grove(now just Pitman) NJ.   Also, they often featured family amusements of various sorts, such as carrousels, roller rinks, and eventually, full scale amusement parks.

There are still a few existing camp villages, Ocean Grove still has revivals during the summer, Pitman still has the revival pavillion, with a number of small streets radiating out,each lined with tiny little houses, and there is a similar, but smaller scale camp at Sellersville,PA--

Here is a description of what used to go on--

Camp Meetings in Early Nineteenth Century