What kind of unit, and where did it break.
Most RV dash radio antennas are the adjustable split ball type. If the rod is just broken off the ball buy a new antenna and replace the half of the ball with the rod (element) on it.
2005 Georgetown 342DS XL, Full Banks Package
2005 Liberty Renegade 4X Toad
1989 Wrangler Sahara Toad
1984 19.5' Beachcraft i/o 5.o liter, 4-bbl (and you thought your Moho sucked gas!)
D/W Carole and Maggie the Teacup Lab (Black Chihuahua)