what to use to prepare wheel arches ??

Bit of a daft question, I can do all other aspects of valeting, but I've never known quite what to do when it comes to wheel arches, and it really lets the job down when you can see brown muck in wheel arches when the sun shines in.
I know most people suggest blasting the dirt out with a pressure washer, but due to our weather (UK) I'm keen to keep the metal protected with underseal through the winter, so I don't want to be blasting it out all the time.
If I thoroughly pressure wash them to start with, and then paint with some nice hard black underseal, apart from wiping the insides with an old sponge, what can I use to spray in to keep them clean and shiny, in the same way as you would spray the side walls of your tires ?

Any help, most appreciated

this would be awesome......is there anything for this?? it would be cool to keep the wheel wells clean without having to take off my tires and cleaning it. could it just be a matter of cleaining and painting the wheel wells with an oil based paint to match the car?? or how bout using caliper paint to paint the insides of the wheel wells? shit, if no one can help me, ima just do it this weekend and see if it works.

I once saw a guy at a car show, he was well into his valeting, is that called concourse ? - anyway, he had a white car, it was absolutely immaculate around the body, but the most amazing thing was how he had prepared the rest of the car. It would have been about 10 years old at the time and covered 50,000+ miles, but now obviously restored
He must have stripped the underside of the car and the wheel arches back to absolute bare metal, then primed, painted to match the top of the car, and then laquered up.
He had a mirror on a 45degree box set up at the back of the car, so that when you looked into it you could see directly along the underside of the car. It was perfect, shiny white....that is 'all' of it, every edge, every nook, the lot, like you'd spent every night for three months under there. You would happily eat your dinner off it (of course that would be hard with it bieng upside down, but you know what I mean !), likewise, the arches were just as good, and even when you poked your hand about inside them, it just confirmed, they were every bit as good
Sounds daft, but it's one car that just stuck in my mind, hard to believe unless you'd seen it with your own eyes, but very impressive
The guy's got far too much time on his hands, what do you think ?

He claims to actually drive it too, I don't believe him, lol !!!!

well....i shouldnt really talk bad bout the guy having too much time....cuz, i my friend, have a lot of freacking time in which i will be looking to do that myself. maybe not EVERY nook, but clean enuff to my satisfaction. hey, maybe the guy does drive it but since he has sooo much time, he probably spends a good hour or two after driving it to clean it. i dont wanna go that crazy myself.....just enuff to rinse them and not be ther all day scrubbing it clean every so often. (by often i mean, ever time i get the car washed or so)