Revo Ram Mount (backing? fastners?)

[pbb]

So my (2008) Revo came used with RAM mount 2000 tubes mounted via 1.5" balls with 2x3" bases just forward of the pockets.

The balls are deteriorating and I bought new mounts to replace them. (RAM has a lifetime warranty, but I recall they want you to send in the failed parts, and I'd rather have spares than have my kayak sitting around with holes in it and nowhere to mount my RAM tubes).

The originals were installed using aluminum pop rivets and no backing. RAM makes a kit for the Hobie's with a backing plate (RAM-301-HOB1). I'm not 100% sure that uses the 2x3 mount that fits older Revos. Hobie currently sells a 2x2.5" (with no backing plate), presumably because later models had narrower gunwales.

I see a few options: 1) try to buy the backing plates and screws from that kit from RAM (assuming they are 2x3"); 2) mount with stainless bolts and use SS washers for backing; 3) make plastic backing plates out of cutting board material; 4) mount as before with pop rivets.

(I can reach the underside reasonably well through the hatch).

I am inclined to go with #2 (SS bolts & washers), since I can reach and since I don't have pop rivets or a pop rivet tool handy, but I can easily get the SS hardware down the block. (But if I did want to go pop rivets, I can borrow a tool next weekend).

Advice?