Normal Black does a very good job. In terms of hedging performance and of smoothness of calibration parameters.Then you can adjust a convexity correction using normal expansion (
http://inflationinfo.com/CPICvx.pdf) or even fit one ala Benhamou , Belgrade market model or Jarrow Yildirim...(but too many parameters dont always make a good model).Then you also need a seasonality factor. A point in time econometric model (ARMAX would do the job) forecasting seasonality factors from CL1 futures as "future regressors" for example would be a good idea.