Over the past two months I've been testing my water slide decals in harsh conditions to see how they hold up and if wax or a clear coat will provide added durability. I applied three decals to an old glovebox lid, giving one a clear coat of enamel, another several coats of wax, and the third left untreated as a control. I subjected them to weeks of full sun—at times over 80°F—and to damp 45°F nights. I dipped them in water regularly to simulate the effects of normal washing. I simulated daily wear and tear by rubbing the surface. The decals showed no ill effects after a few weeks of this treatment, so I decided it was time to pull off the gloves and give them the Extreme Humidity Test. I sealed them in an airtight bag with a few ounces of water and left them in the hot sun for a week. Here's the result:
None of the three test decals fared very well, but then neither did the original paint on the glovebox lid or the original 40-year-old decals on the other side. The glovebox itself started rusting very quickly and the paint began to bubble. Needless to say, if your car was stored in similar steambath conditions flaking decals would be the least of your worries. It's worth noting that the wax didn't provide any protection at all, but the clear coat did help a bit.
Clear coat (left) and wax:
The original Karmann decals began to bubble and loosen too. There was no rust on the glovebox prior to the humidity test.
In the end, I think these tests show that the decals themselves are as durable as Karmann's originals, which is to say that they're vulnerable to damage from unusual dampness and abrasion but should be fine in normal conditions. A clear coat does seem to provide an extra measure of durability and protection from normal humidity, but if you happen to live in a rainforest all bets are off.
If you purchased decals from me and have experienced any unusual problems please let me know and I will be happy to provide replacements.