I'm doing MOST of it alone, with occasional help bucking rivets when my arms just aren't long enough (I have very long arms).
Biggest problem becomes weight and bulk. You get to a point where you need someone to help you position the fuse to rivet, etc. My son in law lives close so I call him when I need him for that stuff.
I'd say, not impossible but better if you can get some help at critical phases.