Hello all, I'm hoping for a bit of assistance.

I'm not sure of the best way (or how to achieve) a tapering cut to a curved part. I've attempted various operations: wrapping a sketch, spline on a surface, lofted boss/base etc etc all with varying degrees of success but none have worked out 100% correctly. Wrapping the sketch was ok for the flat section of the model but went a bit wrong as it approached either end.

I'm tring to start at one end at the full height of the unit (900mm) with a gradual and consistent taper down to 400mm at the other end. I've attached the model and a screen grab of what I'm trying to do..

Thanks
Lee