Originally Posted by TARVIDSON
SSmbs thanks for letting us know about the fit on that G21. Nusslejj, I am very interested in your luck at tapping into something solid there. Keep us posted.
It turns out there is about 3/8" to 1/2" inch of drill-able metal under the sill plate near the inside edge, and it continues along the entire length of the plate.
I still have no idea how that plate is mounted to the RV, but was able to drill with a 13x64 bit and tapped 1/4-20 threads, then screwed in 4 stainless 1/4-20 screws.
I think 1/4-20 is a good size - not too small, not too large. Any larger and I suspect you could miss the metal underneath.
It is now absolutely secure. No rocking whatsoever.
NOTE: I had to place the outside left and right holes based on how my tap-tool handles could swing. The door-hinge side I used an L handle tap (smaller one) so I could get as close to the gas-shock nubbin as I could. That took time to disconnect/reconnect on every turn. The other side I just used the T-handle, as it just works better. It is not perfectly spaced because of that, but I think it looks fine, and certainly fixed the problem.
Because I believe over time the combination of the gas shock on the door and normal foot traffic on the edge of that aluminum sill plate will work it loose (it has to), the factory should consider this solution.
One other thing I will probably do - I'll probably remove the other small aluminum sill plate and replace it with some black caulking. I think it looks out of place, and after you remove it you see it doesn't really cover much - just a fairly small gap.