My last trailer was a triple E ,would of bought another in a heartbeat if they made a bigger model.(do they make any now?)
That said nothing wrong with I beams , because just calling a frame a I beam is not enough information,
like how thick are the webs? how wide? material hardness. cross members ?etc etc
I have seen 2 sheet metal 'C' channels tacked together called I beam.
Stacked square tubes like a mobile suite are stronger(stiffer) PER POUND then a I beam ,but a I beam can be just as strong ,but with a weight and size penalty .