Measured the antenna against the current one on our trailer and this new one will direct fit the old mount holes on ours. The screw centers are
2 3/4 inches apart. The installation would be plastic ring against the trailer - then the metal reinforcing ring - then the antenna base.
When the antenna arrived it was off center to the mounting holes but, that was easily corrected by loosening the rear nut and realigning the mast to the base.
The mast is stationary and does not extend like the original. A pic of the mast we purchased at Advance Auto parts is shown if you want to replace the mast on this new one. I used it on our original base last year, as you can see in the photo, to replace our beat up original mast.
Antenna is part number HS519L. All the searching and it turns up for $10.99 with free shipping. Enjoy....
RV Audio Accessories | Jensen RV Direct