Looks like "billet aluminum" to me. What the heck is billet aluminum any way?? I've been in the machineshop business for 35 years and never made anything out of a billet. Just about all aluminum starts out life sometime as a billet i guess, unless of course it happens to start out as an ingot. The one that really gets me is "Aircraft grade 6061-T6" They just don"t make airplanes out of 6061. And don"t get me started on chrome-moly.
Any way, Nice job and when you are not carrying your tent it would be a good place for a second passenger to stand.