You can read about the RVIA here:
http://www.rvia.org/
Here are a couple of quotes from the "about RVIA" page:
The Recreation Vehicle Industry Association (RVIA) is the national trade association representing recreation vehicle (RV) manufacturers and their component parts suppliers who together build more than 98 percent of all RVs produced in the U.S.
RVIA maintains an inspection program to monitor compliance of the plumbing, heating, fire and life safety, and the electrical systems of the RVs manufactured by its members in conformance to the ANSI/NFPA 1192 standard for RVs. RVIA also provides an on-going Federal Motor Vehicle Safety Standards (FMVSS) education program for its members.
Essentially the RVIA sticker on the side of the RV certifies that the manufacturer built the RV to RVIA standards and that RVIA and the manufacturer will monitor the RV model/brand and report any deficiencies/safety defects to the appropriate federal agencies which track these problems "for the consumer"....
Pretty much, the $135 "fee" goes to pay for the organization, the manufacturer's costs in compliance with the organization and in administrative fees associated with belonging to the organization and maintaining records required to follow RVIA guidelines. There are some similar "stickers and fees" in the automobile industry. One that comes to mind is SAE standards. The Society of Automotive Engineering establishes standards for manufacturing cars/trucks, but there's no "sticker to certify compliance" and no "cost for the sticker" listed on every car. Possibly, (my thoughts) putting the sticker on every RV is a way to "charge another $135 that goes into the manufacturer's "profit margin". However, without the sticker, it would be difficult to get financing from most sources since banks require a "standardized product" before they will loan money, so without the sticker, it would be difficult to find a bank to finance an RV loan.
RVIA is a "privately funded organizational watchdog organization" somewhat like JCAHO in hospitals and the National Fire Protection Agency in the insurance/fire prevention arena. There are a large number of other privately funded "watchdog" agencies, far too many to even begin to name them here.