The blade I purchased had a hard plastic cover which, when twisted, allowed access to the end of the replacement tape measure element. This is experience speaking. The spring steel popped out, inflicting a nasty cut on my thumb. The RG58 coax feedline is connected directly to the driven element. No matter what method you use to attach the feedline, make sure you scrape or sand the paint off the tape measure element where the feedline is attached.
Most tape measures have a very durable paint finish designed to stand up to heavy use.
You do not want the paint to insulate your feedline connection. If you are careful, It is possible to solder the feedline to the element halves. Care must be taken since the steel tape measure does not solder easily and since the PVC supports are easily melted. You might want to tin the tape measure elements before mounting them to the PVC cross. I used a bit of rosin flux to help with tinning the element connection points.