I took a 10 foot by 48 inch piece of sheet metal and cut four 12 inch wide pieces out of it to make a rectangular boxes to put around the wheels. Used four 90 degree bends in it to form a rectangle of the proper sizes. Around the front suspension I had to trim it down from 12 inches a couple places for a fit. The extra length gives me lots of overlap to of the two ends to clamp with a small clamp.
For the jacks, I just use 12 inch metal flashing off a roll to form a circle around each jack. Those are tricky to get a seal at the bottom if you are using boards under the jacks - unless you plan ahead.
For those who say seal all the holes going inside the rig, what about those nice rubber hoses on top the gas tank? And those plastic air lines for the air bag suspension (which I have on the rear)?