I use the Christmas lights too. I use two bulbs in parallel, just for redundency.
I use 400 grit sand paper on the bulb leads to take any dirt and oxidation off.
Break each bulb and use a small pointed tweezers to pull the wrap of wire off the base of the filament posts. This is what allows current to flow through the bulb after the filament burns out so the rest of the bulbs in the string stay lit. If you don't remove this, the bulb will still show a few ohms resistance even if the filiment is open.
Check continuity of the bulbs.
Then hot glue the bulbs side by side on a 2" x 3" piece of paper. Use a size large enough to make two to three wraps and long enough to hold the size charges that you need.
Wrap the paper around the bulbs and hot glue it together.
Twist the leads together with some 24 ga wire and solder each set of leads to the wire.
Fold each wire and lead along the side of the tube and put several wraps of tape around the wires.
A put hot glue in the end to cover the bear wires and seal the tube.
When ready to use, pour in the measured amount of BP, fold over the paper and add a piece of tape to hold it down.
These are a little bit of a PIA to make, but you can make a large number at once. Just complete each step on all the bulbs before going on to the next.