Casting plaster for Lost Wax - Part 4

I have now created 3 wax pieces that are worked over a solid plaster core to varying degrees of success. The process of making the core is very lengthy; preparing the casting bucket, mixing the plaster, vibrating the plaster, fixing in the metal arm and letting it set. Once set there is a lot of carving and shaping work to get the desired shape with a lot of waste material. 

Is there a better method?

I’ve had a few ideas of how to either reduce time or materials or both.

1. Balloons - Filling a strong balloon with the plaster that would give a nice smooth shape without the need to carve. How would the balloon withstand the vibrating? Could the metal arm still be fixed into the plaster?

2. Cardboard - Make the shape in thick cardboard, reinforced with parcel tape. The plaster is poured in and the card can be cut away once set. There still would be some degree of carving to finish

3. Lego Bricks - One of my artist friends who makes Glass art uses Lego bricks to make her walls for plaster casting. Would this be able to withstand the vibrations?

4. Sand Casting - Now I know this would not work as the vibrations would dislodge the sand.

5. Plastic Bags - Much like the ballon idea could a bag be moulded in some way by knotting off areas of the bag to create the rough shape? This would need support during vibrating, perhaps with foam. Or would the bag simply sag into the foam. Perhaps the bag could be suspended?

6. Latex Moulds - This is a method that once a shape had been designed could be used repeatedly to create a shape that is smooth, requires no carving and most importantly reduces waste and therefore reduces cost of materials. Only snag, I don’t know anything about making latex moulds.

Conclusion-I need to try some of these and research the others.