i coat my underside in innox for rust proofing once every 6 months or so, and inbetween i coat the underside in a mixture of silicone spray and tire shine to keep it shiney and new looking, i find this makes it alot easier to clean the underside and keeps most of your every day grime from sticking to it also. then when i come back from mudding i just get under there with the karcher , i dont have ramps so i go to the local car wash which has ramps spend about 2 bucks getting into the places i cant at home and thats about it, when im done i coat it all in tire shine to make it back to black haha
i also put the hose in my chassis rails ot get rid of any mud or sand too :\