I updated my bandpass filter and have included the bode plot below in Figure 1. It is a fourth order elliptic bandpass filter with a passband ripple of 1dB and a stopband attenuation of 30 dB. It emphasizes the area between 3 and 40 Hz.
Below, I applied this filter to the huddle test data. The results from this were only slightly better in the targeted region than when no pre-filter was applied.
When I pre-filtered the mode cleaner data and then used an IIR wiener filter, I found that the results did not differ much from the data that was not pre-filtered. I'm not sure yet if I'm targeting the right region of this data with my bandpass filter, and will be looking more into choosing a better region. Also, I am only using certain regions of ff when calculating the transfer function, and need to optimize that region also. I uploaded the code I used to make these plots to github.