I got this reply from iRV2 Forum which is a Winnabago RV web site. Says same thing Paul said..
"The 4 Wheel Drive can be towed 4 down
The ALL wheel drive can not.
Same is true of Jeeps.
The reason is that on hard dry pavement the front and rear wheels will often have a different rotational speed Also the right and left (Front mostly) this is because of the way the vehicle corners.
On a 4 wheel drive, the two drive shafts are hard linked or.. in neutral completely separated from both each other and the transmission.
On the ALL WHEEL DRIVE, power transfer is handled by automated devices and torque converters, (Fulid and/or electromagnatic clutches) and though you can LOCK it in 4WD mode (Jeep at least) there is no Neutral.. And thus no towing
Not 4 down
Not 2 down
Trailer only."
RR