With a rig that big it will be easy to get into gas stations mainly because you will be mostly limited to truck stops. Towing I don't think would be much different - more stuff to pay attention to though like weights. That brings me to the next deal - a 39+ foot toy hauler will bring a massive ammount of weight with it so make sure your truck will handle it ok. Really 39+ TH is 1ton dual wheel territory.
I would recommend the Desert Fox because of the quality but that is a tow behind and not in the lenght you are considering. The only thing I've really heard of people saying regarding TH brands is to generally stay away from Dutchman. If I were in the market for a TH FW then I would go with Heartland's Cyclone or Road Warrior.