We do not want to use the antenna, what range do you think we will get without the antenna?
If the transmitter and receiver were well screened so that there was no radiation leaking from the enclosure or from the power supply wiring, near zero.
In fact, instead of the proper antenna, we may just solder a 17cm bit of 7/0.2mm wire to the antenna pin.
Contrary to popular opinion, "proper antennas" do not have magical properties. The main advantage of a proper antenna over a bit of wire is the physical structure.
Your choice of 17cm of wire is fine, its physical disposition should be as straight and as far from other conducting objects as possible.
For best performance you also need "the other half" of the dipole antenna, presumably the 0v line of the radio will be connected to one of the power wires to the LEDs.
As for what range you will get from this, it is nearly impossible to say.
It is possible to do some signal path loss calculations to predict the received signal level, but this only works for an unobstructed path. Mounted on a truck (big sheets of steel) the path loss is anyones guess.
How are these beacons to be powered?
Battery or from the truck (24v ?) supply?
I vaguely remember a thread* here on ETO where something similar was discussed.
It involved a low power UHF radio which worked well but was enclosed in a metal box. I will see if I can find it.
JimB
* On edit, here it is:
https://www.electro-tech-online.com...t-antenna-inside-alu-box.142517/#post-1195847