Converting my dully to a 10 wheel drive to handle Toyhauler

To OP....we have a semi truck trailer at work...it is 40 feet long...it has 2 sets of duels on real of trailer...they instaled a tag axle kit to the rear (that looks like it came in a complete kit)that is single wheel ( like a dump truck tag )that is air powered and ride...if you had something like that on the very rear...if in the up position?..your truck would drive as original...but soon as you drop the fifth wheel on?...hit the air switch and drop the rear tag ..this would be easy and way cool?...just my 2