Symbolism, Imagery, Allegory
If you thought the Munsters were the only ones who drove around in a hearse, you'd be wrong. Turns out upholsterers from western Ohio do, too. Apparently, it's actually pretty normal for upholsterers to utilize death cars—according to Mr. Browning, Karl's boss, "used hearses were cheap, had wide back doors that opened all the way, and came with tackle for handling big, heavy objects" (10.30).
It also, though, creates somewhat of a spectacle. You know the first thing everyone thinks of when they see a hearse parked in front of someone's house, and that's exactly what happens on the couch pickup we witness at Rose Carson's house.
"In a place like Republican Corners, everyone phones the neighbor," Karl says of the neighbors' reaction to the hearse. "So now pretty much the whole local population was hanging around […] waiting to get a look at Mrs. Carson's corpse" (10.66). Browning, of course, loses his mind over this and spends the rest of Karl's work time before school ranting about it.
Okay, so the guy is nuts and drives a hearse. What's the big deal? First of all, an old dude driving a hearse is packed with cultural meaning (Harold and Maude, anyone?) and loaded with symbolism all on its own. Way to dance with death, Mr. Browning.
Second, it feeds into the theme of friendship in the novel and how friends need to be appreciated for who they are and what they are before it's too late. "When you get old, the only thing you got left is your friends," Mr. Browning tells him as they drive away. He's willing to stand up for Mrs. Carson when people are standing around the hearse thinking she's dead—so Karl can get over his need to be normal and stand up for his friends, too.