This company has a few different options of these. I got one for my 13 when my headache rack wouldn't play nice with the toolbox and fifth wheel hitch. For an antenna, it should be fine. A lightbar (Whelen mini century) is too heavy for the design.
I don’t think I would trust that to not leak. Last company I worked for ended up buying back racks for all the trucks to mount lights and antennas to. After the half assed round magnet wouldn’t work and destroyed the paint on all the brand new trucks.