Is this this line along the bottom intentional?
I'm guessing that you did not intend to have any mesh there, so that needs to be fixed first.
When you construct the "hump" to subtract it from the block, make the hump protrude below the block and be wider than the block prior to the subtract. That will guarantee that you get a clean result for meshing.
After the geometry is clean, use a method Sweep and pick the body, and pick a Source face, which is the face we see in the images above. Once you have the Sweep defined, RMB on the Sweep and pick Inflate this Method, and with the Edge filter, pick the three edges you were pointing to where you want the inflation.
If you have difficulty, please attach a Workbench Project Archive .wbpz file to after you reply.