We don't use valve extenders on our 16" outer wheels, but we do use them on our inside wheels. First try was these, from Amazon:
They were not solid enough for us and I was worried about adding that much extra weight to one side of the wheel. Rather than use their metal clamps I tried zip-tying the braided stem in place. That didn't seem to work well at all. Instead, we ended up buying these:
I had to pull the outside wheels off in order to install both types of extenders, but I'm satisfied with the second type, the hard metal. We do have to use a longer air pressure gauge to reach the inside valve stems, but that's no issue at all. This is the one we use:
I didn't buy the air pressure gauge at Amazon. It came from a local car parts store, but I found it on Amazon for illustrative purposes.
Hope this helps. Enjoy your travels over there, and keep your eyes open. Getting weird everywhere.