Okay, thanks Luvs3rds, Mac + silvertones for your assist.

Luvs3rds, I'm tending towards buying or constructing a cabinet. Only prob is that Polk recommend a nearly 9L enclosure. That would be about 2 US gallons, more or less, and means more weight and less space in the boot (trunk). However, if that's what it takes...
Moreover, my auto enthusiast nephew tells me that if I were to cut or drill into the parcel shelf to mount the sub it might affect the cars roadworthy status ( and thus insurability).

Silvertones, the bridging would be done using the external switch on the amp which provides for this (and suggests the amp designers are allowing for a mono use, such as a sub). I can't get hold of the manual for this amp, too old, but am assuming that if it is bridged using the external control, that ohmage applying doesn't drop below the 4-8ohms range printed on the side of the amp.

Mac, your guidance is appreciated. I take on board your idea of running the amp in unbridged mode. However, the available subwoofer signal from the head unit is a one lead mono affair. If I run the amp unbridged, won't that mean that only one side of the amp, either the L or R, will deliver wattage to the sub, (at a maxium 35W RMS) even if both pairs of amp outputs are connected to both pairs of inputs on the sub?
I would have thought that utilising the amps internal bridging mode (with the switch Aiwa provide on the case) would enable a mono signal, into either L or R, to exit the amp as a dual mono signal of up to 35 W RMS through each of the amps L + R outputs...unless for some reason it actually means you get an up to 70W RMS output out of ONE only of the amps outputs. And which one? Presumably the same side as the side you put a signal into...but that strikes me as too "suck it and see". The Japanese are better engineers than that.

I don't have an active crossover but provision is made for that on a "software basis" by dialling that into the head units menu of settings, once it detects the sub is connected. You can select (from memory) 50/80/120/160 hz as your desired points.

Finally, I note your comments about capacitors and will keep that in mind. Haven't seen them myself at auto stores but will keep my eyes open for them.

As always, thanks very much chasps.

J.