The search will result in lots of comments about Keystone and Passport, for some reason, there has been a recent influx of people complaining about them...not sure why, they are a very popular unit. I think Keystone build great units.
In terms of this being 1/2 tow-able..certainly it is. This unit is around 26-27 feet long and dry weight around 4700, say 6000 max loaded. No reason a 1/2-ton cant pull that.:h I pull that same length and weight with no issues..Beware of the weight police...:R
For winterizing, most newer trailer come with a by-pass valve near the pump so you can take directly from the pink anti-freeze jug rather than wasting lots of jugs poured into the fresh water tanks. If not, it's really easy to install one. Many folks use the pressure blow out process with an air compressor, but for our Canadian winters I prefer the "pink" anti-freeze to be sure.
Good luck to your son, I am sure they will enjoy that trailer.
2011 Kodiak 240KSSL
Husky Center Line WDH
2014 Dodge Ram 1500 4x4 Outdoorsman 3:92,8-speed,5.7L HEMI
2007 Kodiak 214 HTT (prior)
2010 Dodge RAM 1500 4x4, 3:55, 5.7L (prior)