Ah, you city slickers.
It's not just plumbing size.
Having grown up on a farm with a septic system we never had a garbage disposal. Septic systems don't handle that kind of waste very well.
While many RV parks may be on city sewers I would bet a lot are on septic systems and they would be quite unhappy with your conversion.
http://paradisevalleyseptic.com/can-...septic-system/