Use a small zip-tie and attach it to the body clip,cut a short length of fuel tubing(nitro)about 20mm long. Slip the tubing over the zip-tie and use a second zip-tie to secure the tubing in place,then simply trim the ends off.
I tried the plastic washers, they didn't seem to help anything. Maybe I used them wrong, though. I tried floating above the body, floating below the body, and shoe-gooed to the inside of the body (with and without drywall tape) None really helped.
I was a bit concerned they wouldn't work on the rear of my granite, because there isn't much to drill into, but they have held up just fine. The front was no problem, plenty of meat there. Definitely worth the effort, I didn't realize him much of a PIA body clips are until I tried these.
Those proline screw on caps work best with a new fresh body. They will work with the Arrma pre existing body holes, but not the best. Their will be a lot of slop.