Well, totally bummed, now. Stopped in at the RV lot to check out Rocky and put a cover on the A/C n the roof and take measurements for the pipes underneath.
But Forest River has the entire bottom covered and sealed. The only frame I can see is at the very front and rear bumper...and no way am I cutting into it.
I've read in other post about people cutting into that cover. It's just there for wind resistance and to protect the infrastructure underneath. I think you need to try to find the frame and cut where your brackets will go. You have a 2904ss right? It's the sister model to my 2905ss. I pick mine up in the spring. Let me know if you try this and how it went.
1/4" self drilling/tapping screws about 1-1/2" long will go right thru the metal trim and thru the 1x2 wood that is screwed to the bottom of the frame that holds the coroplast cover. Just make U brackets.