I have made about 15 or so molds out of plaster of Paris and out of resin.I can say that I am pretty strict on my mold making, I like to have nice clean molds that have straight sides so I dont get any kind of flash or crooked edges. I usually glue my plastics down to the container with either some super glue or double sided tape, I also like to mix my plaster so that it is a little more thinner than pancake batter, I feel I get better detail when the plaster is a little more on the liquid side. Once my molds are set I let them dry for about 2 days to get all the moisture out, they will seal alot better if completely dry. I like to take a exacto knife and clean up the edges before sealing. I use Devcon 2 ton epoxy,it is great for some molds,if I have a mold that has alot of grooves,appendages and what not I use Elmers glue mixed with water. If you have any questions you can send me a message,I will help out any way I can. Good luck with your new hobbie.