With a long overhang I don't think I would mount anything at the rear of the coach. I would simply just use wheelwell mounted flaps approx. 3"-4" off of the ground.
On a coach with a shorter overhang I like the rear mounted flaps but tucked up under the rig a little bit. This is critical to keep it around 5" or so off of the ground, otherwise as the rig porpoises slightly going down the road the flap will touch and create more flying rocks/debris than without anything at all.
This also may or may not completely prevent any rock chip issues. I have towed our last couple of Jeeps for 100k plus miles with barely any chips to the front of them. Both were either stock or only 2" lift with 31" tires. However, our current Jeep Wrangler Unlimited with 4" of lift and 35" tires got quite a few small chips and a broken driving light during last years flat-towing. This year we mainly hauled it in our enclosed trailer but for short quick trips the trailer is a bit of a nuisance so I just installed a Tow Defender by Roadmaster. So far I like it.
Here is a link to the thread I just did on it.
Roadmaster Tow Defender