GM250-
First, some questions. How dirty is the compartment? Are you trying to get rid of all the old dirt for a show-type of look? Are doing this in the home, at a car wash or at the shop? The stuff you're going to wash off could include hazardous material and you may not want to wash in down near a fresh water supply (like a stream or river).
If you're working at home like me, I started by hooking up a hose to the HOT water outlet in the laundry and sprayed a lot of stuff off with HOT water. For oily areas on the engine, I used a parts cleaner, small brush and lots of elbow. If you wanted painted areas of the fender liners to come clean, you might use a laundry or kitchen detergent to cut the grease. Also, be prepared to get dirty and wet! In the end, you'll be happy with the results!
Good luck!
