how i drow this only surfacing....in creo,catia or ug/nx....
This is one way to do it fast.
I made it approximately clear, as few dimension are mentioned.
I made it approximately clear, as few dimension are not mentioned in the sheet.
Instead of using BLEND in the middle. you can go by taking a profile and filleting then.
I think this wont take thickness in the bottom side, so for that you can change(decrease) the fillet in middle slot.