I'm not sure if I understand correctly. Do you want a % share of Season=DECRO on total Season and Season=NONDEC on total Season? If so, you can do this without set analysis, using the TOTAL qualifier. I can't write here exactly what you need, because the dimensions are not fully visible on the picture, but I'm sure you'll be able to adjust this:
Sum(Units)/Sum(TOTAL<[Consol MFN.Trai...],[Consol MFN.Car...],[Consol MFN.DLV...]>Units)
fill in the dots according to actual field names.
Hope this helps.