Using Rain Dance Amoonguss
over Volbeat can help relieve your weakness to Fighting-types like Sawk and Gurdurr since Volbeat is not the most reliable answer to them. With Regenerator, Amoonguss can come in multiple times during a match to check the aforementioned Pokemon and set up rain.
Seismitoad should be running a Timid nature
to beat weakened variants of Ludicolo, a common check to rain teams. You don't lose any OHKO from what I know, so it's definitely something to consider.
Summary of changes:
Volbeat —> Amoonguss
Timid nature of Seismitoad