Many people ask me , “What is the best way to tow a GMC”. Thats a very good question in that the coach is so low to the ground. Hope this helps you if you ever need to call for “Mr. Hook”.
Don’t do this, 
while it’s the right idea of not dragging the tail, DOT frowns on the height and the front wheels of the flat bed will leave the ground when you hit a dip!— not very safe.
You CANNOT use a “strap or frame lift” truck either, the problem is by the time the coach is lifted by the front enough for the front suspension to bottom out even with your rear suspension pumped up as high as it will go, the holding tank and rear bumper ends up being a target for every cigar butt left on the road.
A “wheel lift” tow truck will do OK, these have a cradle that picks up the front wheels and drags the coach that way. At least the coach is not towed at such an angle that the back end is not in harms way.
BUT, the best way is with a “Landoll” tractor trailer rig like this one. 
Steps Towing out of Tampa maintains a superb stable of these babies and they have the expertise to use them. OK, the coach is off the ground but there is something more about this rig. Getting the coach up onto the platform without damage is the trick and this thing is awesome. 
Step one is to back the beast into the drop zone, the driver needs that skill, then the fun begins. The wheels of the trailer move forward on the trailer reducing the drop angle. The tongue and tilts and the trailer deck softly angles back. 
The wench gently allows the coach to roll off the back of the trailer. 
The the trailer pulls forward and the front wheels touch terra firma and the eagle lands 
YES, this is the more expensive tow and many do not have this equipment but the damage created by a sloppy or improper tow would easily pay for the extra time and expense of finding the proper hook. The owner of this coach rationalized perfectly that the amount of the tow would be a drop in the bucket when compared to the final expense of the renovation we will be doing and having the least amount of damage to repair will actually help the bottom line of the renovation. Last week we had a coach come in on a frame lift truck and as soon as we get the windshield replaced along with restowing everything that fell out of the overheads, I hope to have a good coach to start work on.
Insist on a “Landoll” trailer to tow your GMC, it’s the best and safest. If they don’t have one or gave you any grief, a heavy duty “wheel lift” will also tow a GMC safely but try for the landfall.
Hope this helps