Big_Eddy, It sounds like you are describing a totally different animal than I am describing.
When asked about using channel for the tongue, I'm assuming ev372 is talking about using a 50 degree A-frame coupler with the channel standing with the 3" side vertical. A lot of people use this method and it works for them. I on the other hand don't like channel tongues for a number of reasons. The first being the channel has a square edge and the mounting area inside the coupler is rounded. Second is the fact that the wiring harness can be concealed much better, faster and easier, and third reason is that I believe channel flexes more than the box tube. Fourth reason , it's my personal opinion that box tube is easier and neater to work with. Depending on the trailer I use 3" x 2" x 11 ga. or 4" x 2" x 11 ga. box tube and in some cases I will use 6" x 2" x 7 ga for heavier trailers. For the basic utility trailer 2x3 will be more than sufficient.

The tongue you described is a straight single tube coupler and is something I would never consider using on any trailer I build. Dave