i dont have a ute but...

i was thinking, have you seen the parcel shelf some 1200s have under the glove box? if not go look at one

maybe you could take that out and bolt in a box which had say a 10 inch woofer just pointing down towards passengers feet, wouldnt be a huge box but maybe enough for some 10 inches and not exactly prime positioning, but how desperate are you for bass

found pic of my car showing parcel tray (in coupe)

parcel tray to be replaced with doof doof