I found a way of holding the hard line pieces together at their cut ends so that they can be trial-fitted into the chassis. Masking tape let the pieces fall apart so I tried using some aluminum foil tape that I bought at Home Depot-- voila! it worked like a charm. one photo shows how it is used.
The tape must be removed for welding the joints, but before the tape comes off, I made some index marks with a penile device punch on opposing ends so that I knew how it needed to be held in position for welding.
The silicone couplers and T-clamps are looking like they will make good connections between the 1.5" stainless tubing.The Ty-Wrap is temporary-- there will be clamps to hold the line in position on the chassis. I bought them from Columbia River Mandrel Bending-- good prices & fast shipping.