Had the same issue on all 3 of our vans, always cleared after a few trips as it gets warmer. Unless it is a more serious amount of condensation rather than just light misting I would just leave it to clear itself.
We had the same problem, the advice we were given and followed with successful results was to remove the little bung in the corner on a very hot summers day, leave it in direct sun light and replace the bung before the sun goes down.
As above unless the bungs had already fallen out or been remove previously.
You could get a small can of argon gas and fill it with that instead.
Take both bungs out and use a small tube in one hole from an argon gas bottle. GENTLY open the tap and just run it for a minute or two and then replace both bungs with a little bit of clear silicone to help seal them.
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