I've gone for a 1/3rd scale mock-up... the late Belgian conceptual artist Panamarenko was a great fan of the Great British 'mock-up'.
For alloy tubing I've selected Simmal's (Preston) 1" by 18 swg, five metres off at a cost of £18, thank you. These I've cut to 24" apiece, and insert into Cotel's (Barnsley) three-way tube connectors, model 8061. They're German-manufactured and come in a steel-reinforced version for big boys' (or girls') toys.
The tube-inserts in question will fit the next gauge up (1/16th of an inch) more closely, and so here I've inserted a touch of silicone/mastic/caulk to take up the slack.