You are right in that a $500 variety of subwoofer may be a little too much for those amplifiers to control.
A bandpass enclosure has an inherent steep lowpass filter that can make distortion inaudible until the damage is already done, especially if you have an enclosure within an enclosure (as in the seat console).
Its hard for a bandpass enclosure to be linear (relatively flat response) and still deliver a substantial boost in output for more than 1 1/2 octave. They can sound great but I doubt you could do well by using an off-the-shelf version. Those, like most off-the-shelf bass-reflex enclosures, are generally designed for maximum peak output rather than sound quality. And its harder for the output of a bandpass to seamlessly combine with your fullrange speakers in order to get decent bass tonal construction. While its all very possible its not likely to happen without a professional design throughout and a custom enclosure.
I would simpify the system by placing all bass drivers in a single optimum location, if for no other reasons, efficiency and phase coherency. You could have multiples behind the existing free-air woofer which could be removed and the opening could be converted to a large vent. Or, you could have one SERIOUS 2-ohm dual voice coil woofer driven by dual equal amplifiers (one amp per voice coil).
Start with the ideal location, from there determine the acceptable maximum displacement, from there determine the best enclosure type (whether bandpass, bass-reflex or sealed) in combination the right woofer size or multiples of woofers for that given displacement enclosure. The largest woofer doesn't always win although collective woofer surface area is one of the most important factors in an open boat. The sequence of location first, enclosure second and woofer selection third will serve you well.