I don't have one in my class C, and wouldn't really have room for anything more than a tiny portable model that could fit in a storage compartment and a clothesline or clothes rack.
On a ten week trip a little earlier this year with my mom, we used coin laundries and, at least for us, did not find it overly much of a hassle. We also rarely stayed with full hookups, and frequently without any hookups, so had there been a unit in the RV it would have been hard to use given the tank sizes etc.
Personally, I would generally prefer to use laundromats and have the space and weight available for other things in the RV, even if it's only more elbow room in the living areas. (For similar reasons, I'm glad to have a relatively small shower and bathroom and larger kitchen and living areas. I spend more time cooking and eating and living than I do keeping up with personal hygiene.)
On the other hand, I hope and expect that people who have RVs with laundry equipment would like and use them; otherwise, why bother getting one so equipped?
