Add AGC (automatic gain control) to level out the audio
Not only do levels vary from podcast to podcast, but within podcasts if they don't pre-process the audio.
I suggest active gain leveling, not just simple replay gain or normalization. As though the listener was constantly moving the volume up and down to make it consistent.
Technical: Calculate the RMS level for the upcoming 1/4 second or so, then adjust an internal gain block to either boost or cut to compensate. Response time to loud passages should be pretty quick, then release times to higher gains during quiet passages would take a second or two.