Squeeze some silicone into the mold and use a thin object like a toothpick to spread it and make sure it is in all the little nooks without air trapped inside. Add a bit more silicone (don't need much given it is quite thin) and pop the base on with the little nobs facing down. Note: Some excess should come out the holes on top. If you have access to a centrifuge I find it helps really well to pack the silicone down. It also helps to spread the silicone fairly evenly to reduce bubbles trapped, but a small amount doesn't seem to affect it. Leave to cure, demold and attach handle. I print with ABS so a little bit of acetone works great to glue them together.