Part #'s from McMaster-Carr for the alum tubing:
1) #4568T13 Alum Tube .065 wall thickness and 1/2" od.
2) #9056k631 Alum Tube .035" wall thickness and .305" od.
I use a 21" length with 6" inserts and 1/8" shock cord from REI. Glue inserts in 1/2" tubing. Plumbing fitting for tube to ACME thread for VersaTee. Cut tubing with a pipe cutter for a good/flat cut.
I use dedicated length elevated radials for better efficiency. Std VersaTee, mini-coil, HB guy ring, and colored guy ropes for visibility purposes.
I use fiberglass driveway snow markers (Home Depot) cut to a 24" length and tubing adaptors for the slip fit joints. Simple fishing line swivel adaptor for the top end. I got the "heavy duty (0.38" diameter)" shock-cord 3-section whips custom made from Buddipole. Get the screw-in ferrule for both ends: one end to the VerstaTee and the other end to the mini-coil. The Mini-coil has no screw-in male insert 3/8-24 adapters, i.e. female only so you can screw in the shock-corded whips. The 1" alum rod is a HB "coupler" when I don't need the mini-coil for the higher bands (17m and above in my case).
I tested my setup for each band in my backyard. These are my "starting" baseline configurations. For each of these bands I use the 3 sect Shock Corded whip then coil (if required) then another SC whip or the long Black Whip. Your setup might differ and certainly where you setup in the field will affect these settings, e.g. on rocks, sand, good earth, etc.