My FM antenna is mounted on the roof to a flat piece of metal with a hole that goes thru the center of it. All is sealed up with dicor. The antenna itself is mounted thru this hole and connection made on the inside of the trailer. The top side is a large spring and then a whip extending up from the spring.
You might want to start looking at all of your FM connection starting at the roof and look for something broke. I have hit limbs with antenna on several occasions...
This is not my antenna but looks similar to this type of mount
The antenna connector that plugs into the back of the AM/FM radio may not be pushed in good...
My 2005 Flagstaff 8528RESS which is made by same people the Rockford is gets great FM reception.
If I was going to put up a new antenna I don't think I would go for the roof but mount on the edge and penetrate the trailer wall into a inside cabinet area. I have put several Amateur radio type antennas on the sides of trailer that look something like this photo..
I'm chicken liver when it comes to drilling holes in the roof...
hope this helps...