I think it depends on your situation and what works best for you. I love car topping the TI and I make sure to rinse my truck off as Bob mentioned. I just personally have too many freakout memories with trailers. I was on the interstate one time towing a 27ft Helms on a double axle trailer. One of the axles suddenly split in half. Let me just say if that happens it looks like an action movie in your rear view mirror. I have had plenty of other less dramatic examples.
My uncle was pulling his 24ft bay boat back from Venice one time and while he was singing along in the car he looked in his rear view mirror and nothing. No boat. No trailer. Just gone. The trailer ball somehow shaved right off and I guess he forgot to use the backup chains. Fortunately no accident but found his boat in some thick woods off the hwy.
Just for me personally if I can avoid trailers then I always avoid trailers. With my current setup I have taken 15-20 hour road trips. Stay at 75 on the interstate, have been on windy mountain roads, etc and never the slightest problem. The down side of course ifs the lack of convenience when putting the TI in the water. Also I noticed this T-rack that actually pivots down. I bet this would come in handy for some people - http://www.autoanything.com/roof-racks/69A6612A0A0.aspx