Model the side profile first, then you can mirror it and extrude the connecting pieces. Could use curves for the profile, change the curve resolution, convert to mesh, or just model it as a mesh to begin with.
Model it with sharp corners first and then bevel the corners one by one for the desired profile (mouse wheel or ± keys to increase or decrease smoothness).
Leave the center as an Ngon at first so you can inset it with the bottom to create a nice edge loop that flows with all the corners, you can fix the ngon afterwards but it doesn’t matter much since it’s on a flat surface.