Looks good! That looks like plaster-impregnated tape you're using on those hills. That's okay if you aren't planning to move your modules around town a lot. Plaster carries a lot of weight.
Another alternative is to use Spackling compound available pre-mixed at your local building supply store. It has the consistency of dream-whip and can be made even soupier simply by adding water and mixing it up well. When finished with the plastic tub, simply put the lid back on tight.
The spackling compound will dry in about 24 - 48 hours to the same hardness as plaster but with about 1/10th the weight. It can be worked the same way as plaster.
Something you might want to take a look at.
Bob M.