First, let me give you a little history behind the bike rack you see pictured below. Back in 1993 some friends and I planned a mountain bike trip to Moab Utah. One of these friends owns a 1971 Westy which, with all the camping gear necessary for 4 people, was beginning to look quite cramped. We realized right away there was no way we were going to fit 4 bikes INSIDE the bus. After much contemplation we decided the needed expense of the trip would prohibit us purchasing one of those cheap, off the back, bike carriers. At the time I worked at a major metal fabrication shop, so we put our heads together and came up with a "bomb-proof" light weight aluminum rack made from materials I had available from the shop. The result, as you can see below, is a very clean, non obtrusive rack that can hold 4 bikes securely and can still allow access to the engine (by swinging the bikes to the left and right). For obvious reasons I wanted a rack that I would feel comfortable carrying $2000+ dollars worth of bikes without the fear of losing them on the road :( . By the way, after 5+ years of frequent use the bus's rear hatch is still working and in the condition it was originally and the rack shows no stress or cracking. Several more have been built since the first, including a prototype for '80+ buses. The materials used in these racks are all 6061 T6 Aluminum extrusions (exept for mounting bolts which are stainless steel). The rack is supported by the full length of the rear hatch. As you can see, bikes are mounted by the fork and rear tires can be lashed to the rear bumper for added security. The fork is clamped using ordinary skewers. One plus of this design is the visibility through the rear window and the fact the tail lights are not blocked.
Here's a pic of my friend Steve's bus near Moab (click for larger picture). Notice 4 mountain bikes neatly mounted at the rear of the bus. We spent 5 hours trying to get back to the pavement from Bartlett Wash after a rain storm.