A long time ago, I was given a trailer made out of the back half of a 60's C10. It was very heavy, the bed was very high and tough to load. It didn't tow particularly well, either - but that could of been how the tongue was made. The double snowmobile trailer I use now is worlds better.
I agree with those (and you) if you want to do this, build your own lighter weight frame and use a trailer axle and springs. But unless you really need some sort of box (or even if you do), using the truck body just seems heavy and limiting (for instance, a double snowmobile trailer is 8x10 with a tilt bed and no GD wheelwells).
And in case you think this would just HAVE to look classy: