I have Yakima racks on my FWC. I mounted two 100 W panels to the tracks on my roof.
I think you could use an approach similar to mine for Thule racks
I bought four 1" x 2" rectangular Aluminum tubes cut to length I specified (two for each solar panel) to bridge between the tracks.
I bought two Yakima 8890028 hardware kits. Each kit contains 4 rectangular plates, 4 socket head screws and 4 washers. The plates slide into the track and are normally used to attach the Yakima landing pads to the tracks.
I drilled through the aluminum tubes with a small diameter drill to match the hole pattern in the Solar panel frame and to match the mount location of the Yakima racks.
I then drilled the side I needed to insert my socket (opposite to mounting side) with a larger drill (see pictures).
This results in the correct size hole at the mounting interface and an oversize hole to accommodate a socket on the opposite side.
One needs to be careful when drilling as the solar panel small holes are on one side of each tube (with the Yakima rack large diameter socket holes on that same side) and the Yakima rack small holes are on the other side of the tube (see pictures).
It helps to elongate the Yakima rack holes a little since the spacing may not be exact after drilling.
I screwed two tubes to each panel with 3 screws, lock washers and nuts going between each side (rail) of the Solar panel and each tube. I then lifted the tube and panel assembly onto the camper roof and attached them to the Yakima racks.
The Solar panel position can be changed (slide the panel where desired) or the panels can be easily removed if necessary. There is over 1" of air space under each solar panel and the top surface of each solar panel is slightly higher (maybe 3/4") than the top of the fantastic fan vent covers when the covers are closed.
The 4 tubes cut to length and the mounting hardware all totaled less than $100.
Edit to include image of Solar Panels on Camper roof:
I hope this is helpful,
Edited by ckent323, 23 September 2017 - 06:32 PM.