It will mostly depend on your cage and soft-topsituation. Which ones do you have? Roll bar clamps can be used to give you muonting points for a couple of exo-tubes to strap the boards to. I plan on using the aforementioned clamps for installing a Load warrior rack, so I can put some gear and canoes up top.
My advice would be to put something soft between the top and the board if you dont make a rack...just to protect the vinyl...done this a couple of times for hauling ladders and such locally. But for a real road trip, you will need to add a rack using clamps--whether through the top or a "reach around" setup. If you are willing to pierce the soft top fabric--hence the through the top. In that case, talk to a vinyl shop and have them install some grommets where you will want your bolts to go through to the cage, clamp or bracket. In my earlier comment about using roll bar clamps, I should have stated that this can be done as "reach around", if you arent running side windows; the exo frame would curve up and over the soft top material...not touching it or abraiding the windows. 1.25 or 1.5 " tube would be fine. This is how I plan to do it. I am not a fan of the hassle of having to remove hardware that is through my top everytime I want it up or down.