Recommendations for a compact passive sub?

Hi, I want to buy the coat for the button, i.e. I have a Monacor SPH-250CTC dual voice coil 10" speaker, and looking for a suitable cabinet design.
My existing loudspeakers are dipoles that go down to about 80Hz. I want to build a passive subwoofer design with a single driver, connected the voice coils to both channels. Perhaps I could use a passive filter. The sensitivity should be about 85 dB/ 1W /1m. 35-40Hz lower cutoff is OK.
I was considering a modified Ripole, but that might not be the ideal choice. It should be compact anyway. What else do you recommend?