Two things, since we're beating this horse senseless...
As mentioned so many times, please totally disregard the bullshit "tow ratings" that manufacturers are advertising for their trucks. IMHO we're not long from a major incident that causes the NHTSA get involved and force them to reel in their frankly unsafe stated capabilities. Speaking bluntly - there is zero - and I mean ZERO - chance that those 1/2T trucks should be considered to "safely" tow the numbers that the manufacturers are claiming. I'm not making that statement lightly - I truly believe this. New car/truck dealers are the very last place to take advice from as for what you should buy. I've never ever in my life met a truck dealer that had even the slightest clue. Just here in this thread you've got a number of people who each individually have probably pulled with 1/2T, 3/4T and 1T trucks more than any of the salespeople you'll ever meet - in one year.
Second - Tom is right. If you're buying a trailer that's at least 20' - particularly a toy hauler, it really doesn't cost you much more in any regard to go a little bigger than you "think" you'll want. The cost of the trailer, and the cost of pulling it, are not going to be that much more to go for example from a 20' TH to a 24' TH. So long as you don't get into the much heavier 5th wheel or longer tag trailers that are much heavier, pulling them isn't really any different. As a matter of fact, the longer the trailer, the easier it is to back up to be honest. If you have the room for storage, my advice is don't skimp. You'll appreciate the extra space every time you use the trailer. Personally, I have tons of room to store my trailers, but have limits on turn radius to put it exactly where I want. That's the only reason I chose the length I did - otherwise I'd have gone yet another couple of feet longer. I live on a country road, and have large trees on both sides of my driveway entrance. Particularly when pulling with a gasser, your fuel economy is going to be based on three factors. Frontal area, and weight. Marginal weight increases by extending trailer length do not result in linear fuel economy impacts. Finally, speed/terrain will have an enormous impact.
One other thing to remember. For all practical purposes, a 3/4T is every bit as "drivable" as a daily driver as a 1/2T. Particularly if you're getting the same general drivetrain, the only measurable difference is that the 3/4T will ride a little stiffer - but even there, the new 3/4T trucks ride pretty darned nice. There is one - and only one - reason IMHO to even remotely consider a 1/2T if you're going to pull any reasonable sized trailer. That is that here in PA, your annual registration costs are a good bit higher. I believe my annual registration is $152 but am not totally sure. For me, that only means something if you're only pulling a trailer once or twice a year for a short distance.
Whatever you do, good luck. You're getting the advice because we like you and don't want you and Ria to have a problem!