I used to have a big 26' UHaul truck for hauling my 4x4's. It was like a 2nd garage...and a motorhome. When I was at home, it freed up a garage stall as I could store my buggy inside. When traveling, it was tight on sleeping space, but huge when I was in camp. I did use it a few times for shuttling vehicles and boats. Here it is one time with the shuttle car inside, rafts on a trailer behind:
2 rafts and 11 kayaks, sure!
Raft on top of the Suby, no trailer:
Fantastic for security, storage, camping. As others have mentioned, really not ideal for rigging inside. If you're doing multidays some distance from home, it would be awesome. For a daytrip rig, it would be less than ideal.
Bighorn listed some good downsides...if you get an enclosed and want to launch out the back of the trailer, barn doors (and props to hold them open) would work better than a fold-down ramp door.
Every trailer solution is a compromise.
Your boating style, distance to the river, etc should dictate what you really NEED vs what compromises you can live with.
Another idea would be to build a platform about 2' off the floor. Put your cooler, drybox, oars, etc below the platform and keep a light, slick boat on top. You'll have a bit of rigging/derigging at the river, but this would also make it easier to fill the cooler with ice or to stock boats...or you could even sleep under the deck and leave the rigged boat on top.
Enclosed trailers need a bit of work to make them sleepable--they don't have enough ventilation for people exhaling moisture all night. One roof jack is good, two would be better. Also the doors are designed to be locked from the outside and are not easily kept closed from the inside...and also think about someone locking you in from outside. They're dark as a cave. A few windows high on the wall, small enough for security but large enough for natural light would be VERY helpful.