Transmission1

I made a mobile antenna years ago using 1/2" black plastic conduit about 3ft in length, wound 11 metres of 17A automotive cable around it, tight wound at the bottom gradually getting wider to the top leaving a 'tail' at the top to trim for SWR tuning, the bottom end I cut the head off a bolt, same thread as a mount on a 7" magmount, drilled a hole through it and the conduit, put a bolt through to hold it al together, wound black PVC tape around the conduit and wire to hold it all in place, looked really good on the roof of my mini and worked a treat! I called it a 'thick stick'. Still have it in the shed somewhere.

If you're dead cert on using copper for an antenna, when making the 'ground plane' why not use a bending spring instead of fittings, and a pipe flaring tool so as to 'slip' one piece of pipe into the other, cutting a 1 inch slot on each side of the pipe would allow you use 'jubilee clips' to fix one pipe length into the other securely.
I'm an Old Gas shipper TSE. hehe

Back in the 80's I got a small square piece of aluminium about 6-8 inches, drilled it for a DV base, then on each corner I put a hole to which I attached a 1 meter aluminium tube, bent them downwards slightly thus making a 4 legged ground plane, good SWR's and twigs were interchangeable, i.e. Firestick, DV27, Cherokee DAM, Halfbreed etc... total cost! Not much at all as made from scrap bits..