I tried a couple of canopies, and discovered that the Rub 'n Buff has to be fresh - if it feels grainy, the effect won't look good.
Here's the first canopy and the Rub 'n Buff:
That didn't look good, so I tried with the second canopy.
Here's the "raw" second canopy. It's about 20mm long and not very clear:
One layer of gold Rub 'n Buff applied, allowed to dry then removed (by rubbing with a soft cloth):
You can see the problem; the Rub 'n Buff was grainy (probably drying out in the tube) so there are thicker and thinner spots and a general uneven finish.
I removed the gold Rub 'n Buff and applied silver Rub 'n Buff from an unopened tube. It went on smoothly:
Removed most of that layer:
It's more of a smokey silver, but you can still see through it:
As a second experiment, I wanted to try Tamiya clear yellow, thinned with denatured alcohol. First, I removed the Rub 'n Buff with some denatured alcohol on a soft cloth:
The Rub n' Buff polished up the plastic a bit.
With the thinned Tamiya clear yellow:
As an experiment, I put some of the crappy gold Rub n' Buff on the Tamiya and buffed most of it out:
The gold spots are annoying; it should have been a smooth color, like the silver Rub 'n Buff but some of the gold did give the Tamiya yellow a gold sheen; it's easier to see in person.