There's some pics on here of the guys loading them onto 18' and I think even one 16' trailer, the 18' is marginal but the 16' is nutz!
I've got a 20' car hauler and haven't used it to pull a dually yet but after measuring it out, my crew dually would fit on it, with the back tires up to the rear of the trailer fenders, maximum of 1' of the bed hanging off the back which looks more than fine to me.
If the truck is lowered and you can't lift, might have trouble getting it that close without smacking dually fender to trailer fender, but you'll still have enough deck behind the trailer fender so you're not hanging too far off.
Also pay attention to load ratings and what these trucks weigh! My 20' is a 7,000lb trailer, not sure what typical 16' and 18' are.
Here's my 20' with a 60" cab & chassis, which is 4" longer wheelbase than a standard 1 ton reg cab longbed. The rear of the frame is about butted up to the front of the trailer. Note the amount of room left behind at the dovetail. Also keep in mind if the truck you're hauling is standard height or you can air it up, front bumper can overhang the front of the trailer giving you some room.
Also if you have a place to keep it inside out of the weather a wood deck is fine. Otherwise go for steel and keep up with the paint. Wood decks don't take long to start rotting and it gets away from you fast. My trailer is an '06 model and hardly has any use on it, I bought it used, one small section of the boards is already rotting out (like that when I bought it.) I keep it inside pretty much always. Keeps thieves away, too..