I use a domestic pressure washer on mine about once a month. The car has no carpets and tillet seats, so I've drilled holes in the floor to let the water out. I get all around, under, and in the car inc the cockpit, just avoid the electrics under the scuttle. Pressure wash under / behind the seats, all the grot traps, inc behind the fuel tank ( I take out the boot floor), get into the tunnel from both ends. After letting it drain, and drying off the bulk with a chamois leather, the car then goes into the garage with a dehumidifier for 24 - 48 hrs. When it fully dries out, I'll spray WD40 in all the grot traps, and along the bottom rails in the engine bay. Then wipe over all the powder coated suspension, roll over bar etc with a rag coated in WD40. I polish it maybe twice a year. Car effectively is 8 years old, no corrosion, and all powder coating is excellent. It's used all year round, apart from this year, but I do try to avoid going out when there's salt on the roads. The only problem is with the excessive stone chipping from too much use, high mileage, but that's "patina" and adds character.