I have thought about that in the past.
A few points as to why it would be difficult to put a UHF in there:
The kit and wiring to make the lights flash take up a lot of room, so installing the guts of a UHF would be almost impossible.
Price wise most people would baulk at the idea of paying well over $800 dollars for a UHF/ RVS
Plus the fact it would take twice the time to make etc (again increasing the cost)
(And i should mention the pic you put up is of my first version i made, the newer versions look a lot better..