My Combi rear end attracts dirt and nothing you can do will stop it, it's the vortex? created behind the car as it moves forward.

I did find that the rear window took longer to get dirty after I fitted mudflaps...

Thanks for the replies, I believe it will be a new hatch for me. BTW, rear wiper is included on the estate, but it is an option on the hatch here in Norway (cost NOK 1000/ GBP 100)