That's what I am planning on doing. I was planing on bonding and riveting (like a fighter jet or Lotus Elise), but this looks better, and field repairs are very easy if you just take a propane torch tip and brazing rod with you (not that they should be needed).
With welding, strength comes from a relatively small bead. With brazing you can easily use angle brakets to create lap joins like DIY bolt up trailers, but you can braze entire surface of the bracket to the frame. That's a rediculously strong joint.
The cost of aluminium is quite high compared to steel, and this brazing rod is also quite expensive, so it probably would be cheaper to pay someone to build you a steel frame. Part of the reason I'm going with alloy is that I have a trade discount and I want to do something different. My goal weight is 500lbs (to put that in perspective that's what two push bikes are designed to support), we don't need a massive structure. I will be using things like military surplus Ti bolts though
With brazing being an easily removable joint, it lets me spec light weight members, which can easily be replaced and up rated if they start to show signs of stress. This has less to do wth the strength of alloy and more with my design and testing principal. If something is too strong, it's hard to ever know by how much. If something is too weak we can measure deflection and make a design choice for the replacement.
The same company also sells brazing rod for steel though. That would be cheap on materials and DIY labour
