You can use layers of anti-static foam. The lowest resistance/most conductive should be the closest to the conductive surface beneath it and them as you go out from there each layer should be less conductive more resistant. You can use anti-static foam. How well does it work? Ive tried it but have never been able to test it beyond just subjectively. But it does seem to help.
The following is just for fun/as an experiment.. I'm not suggesting you do this for any commercial product.
You might also be able to make RF absorbent material using a two part foam, activated charcoal (and possibly iron or ferrite powder, but I would suggest not using that, even if it improves its RF qualities- see below) .
But if you do try to do this, plan out the workflow really well and to the second because its hard to mix quickly and hardens to a very tough consistently almost immediately. Whatever clothes you are wearing if it gets on them it will be in these forever. It will be very very hard to get off of anything it splashes on.
Also,I suspect iron powder is likely dangerous inhaling it is likely very bad for you. So i would just use activated charcoal (which I got from used up water filters (Brita) which have a lot of it in them). You need a lot to get a resistance low enough to measure. Which makes the pinkish black "foam" I ended up with as hard as a rock. Its very hard to mix it before it hardens. It hardened so quickly I think for me because the activated charcoal I used was wet. (Dry used up activated charcoal might harden much more slowly)
Anyway, for what its worth, thats how I tried to do it.
Looks good; if you want to fix the enclosure reflection issue there are RF absorbing ferrite sheets like these:
(Attachment Link)
The 3.2 inch clone is just one of the many clone manufacturers that played it fair, and I don't mind recommending it if you want a NanoV2 with a metal enclosure.
OMG this was good ! Not only for Nano but... I have totally forget to try find some this kind of things even more importantly to my some other things... I have direct places for these products after I return my homeland. (not only just in image but they have also other things..)
But for NanoVNA it need experience what exact product and how is best to try -- of course without experience it can find using long iteration... but it is not nice to teardown for several iteration if there is allready some experience..
Even some advisory so that do not start from empty board. What material exactly, they have many, and where exactly add in Nano. There is several thickness and different materials.