EDIT 2 24/10/20: After more than a year outside, up the roof, rain, winds and sun. Going from cold 5ºC days to hot 42ºC, the centerpiece still holding on nicely. I didn't went up to check it closely, but it's definitely still holding pretty well.. Printed in PLA..

EDIT 1 27/09/19: Added two band center piece, I'm planning to use both 2m and 70cm band, so this should be useful. Also added grooves to secure the cable using zipties. I'm using the holes at the back to screw a Pipe Clamp to fix it to a pole made out of 3/4" pvc pipe. The elements are 3/8" aluminium rods and they meant to fit tight on the holes, but if its too lose you can glue it, or if it is too tight you can sand it, but it should fit nice and tight right out of the print bed.

After having a horrible idea about a dipole centerpiece, i came with this, much simpler, works great, 50min of printing, 5 minutes of assembly, ready to go. My last try was this huge and horrible triangle shaped thing:

https://www.thingiverse.com/thing:2992947

DON'T WASTE YOUR TIME!

Tested about 1 meter above ground with 10m of rgc58 cable, gave me excellent results, 1.2SWR at 147MHz.

Dipole antenna box (center piece) for 2m band (or whatever you want). I first designed it to use 8mm rods, but I can only find 3/8" rods in my local store, so I modified the files to use 3/8" rods for the elements. It is very tight, i need to sand a little bit to fit.
For connecting the elements to the cable I drilled a hole and passed the cables through, then pull the rods until the cables where secure. use your imagination to find a better way to connect the elements. I used a metal tube clamp to attach the antena to a pole, and used 3/4 inch PVC pipe as pole. It is an amateur design, I am novice to ham radio and antennas so maybe something is off, be gentle. suggestions are welcome.

Materials needed

2x 3/8" aluminium/copper/stainless steel rods/tubes between 49 and 51 cm long each (for 2m band, tune it at your taste)
50ohm Coax Cable (mine is rgc58)
3/4 pvc pipes
3/4 tube metal clamp
Solder, soldering iron, pliers, tape and all that diy stuff...