Evo I already have a set of 4" 2-way speakers. But given previous advice I'm looking for some 4" splits (separate tweeter) for the front, which leaves me with the spare 4" speakers, so I was planning to use them for the rear. It's only a double cab not a wagon so I'd have thought that would be OK?

I'll be getting a separately powered slimline sub (not sure of brand yet - whatever's cheapest I suppose)

I think given the cab shape and a desire to still allow people to sit in the back seats without belting their head on things rather constrains my options.

Does that sound like a reasonable plan? Any other advice you can offer? Thanks mate.