Need some help fab-roe-katen

I am reracking a piece of equipment. I want to make a stump that this slides over. It is 3x4 so I need 2.5x3.5.
What is the easiest way to get a 2.5x3.5 heavy walled tube.

Can you buy 3.5 channel or I-beam?

Perhaps two pieces of angle iron. Cut them down with plasma. Weld two angles together. Pretty easy project if you want to get metal and come to the house one evening.

Get some 2x3 and weld a piece of 1/4" flat bar on each side?

What about 2.5" square and weld on 6 pieces of 1/2" x 1" x 3" weld on 2 pieces at the top and bottom and 2 in the center. These pieces would locate the outer tube but not have to run full length.

Basically 2.5" tube x ?? feet long and 18" of 1/2" x 1" flat bar.

Bender mount?

Dam me and Jduck think a lot alike.

Either angle welded together as John suggested or see if Besco has rectangular tube in that size.

How long does it need to be? I have a few feet of 1/4" x 4ish inch angle you can use but I'm out of town for another week.

All these ideals Ive tossed around. I was just hoping I overlooked simple. I leaning towards 2x3 with 1x1 angle welded to the outside corners.

Done-diddly-done