That should make a pretty nice one. Especially with TIG welded joints.
Wherever you need to put bolts through it you may want to consider making tube spacers for sleeves or sliding close fitting blocks of hardwood into the area that the bolts go through the tubes. It doesn't take a lot of tightening to see the walls bow inward without some sort of support inside.
Try it on a sample piece of tubing without supports first, and then decide whether the supports are needed or not.
I didn't care for the pine 2x4 construction called for in the Solsylva 25x37 plans and used red oak for my 1st build with no regrets.