Hi @Costas, sorry for the delay. Arrived in Spain a couple of days ago and couldn’t remember where my box of M3 Nylon fixings were.
Apologies for the poor quality of the photos, taken on my phone.
The Wemos triple base I had to hand had quite long solder pins sticking out of the underside. Rather than trim them down I thought I’d demonstrate how to overcome that issue - handy for those of you that are somewhat challenged in the soldering department 
I used an M3 nylon bolt, plus a nut to give the extra clearance on the underside, then a hex spacer as the way to pinch the board down tight:
You could use nuts instead of the hex spacers, but then you’d need to use a nut driver or long nose pliers to tighten/loosen them. Much easier to use the hex spacers as nuts so that you can grip them with your fingers.
The Wemos double/triple bases have more clearance between the holes and the socket strips at the bottom (in the photo) than the top.
This makes it a bit trickier to tighten/loosen the hex spacers at the top, but it’s still do-able with the ones I have (bought on eBay from China).
On the bottom of the board is where the heads of the bolts are, and I put a blob of epoxy in the head of each bolt then turn it over and position it on whatever it is I’m mounting the base to:
Once the epoxy is set you can remove the hex spacers and the Wemos base, and add more epoxy if needed. But, if you’re happy with how it went together then just leave it as it is.
You don’t want bolts, or hex spacers, that are too long, as they will foul the Wemos or whatever accessory it is that you try to plug into the base.
I used M3 x 12mm nylon bolts and M3 x 8mm nylon hex spacers, plus M3 nylon nuts in this example.
Pete.