I did used to have a pair of worklights on the back switched from a 2way and off switch so that I could select them to work with the reverse lights or control them manually but the worklight I have now is just switched manually on the dash. There are some legalities with regards to the wattage and number of lamps for reversing - I think, going from memory that they could be no more than 21W so a 55W spotlight was a bit questionable!
If you want to wire it up you need to run a fused feed to the back end (you could probably use the accessory feed for the aux tow socket if you don't use it for towing) to a relay and break into the reverse light feed to switch the coil on the relay - plenty of wiring diagrams on the net for how to wire up a relay, pin numbers etc.
Might be an idea to fit a switch so you can turn it off just on the off chance you're reversing out of a parking space in front of a copper who knows his stuff :lol: