Could I use a clean 32-40 gallon trash receptacle to store RODI water for a saltwater aquarium?
As long as the container can handle the stress of 30-40x8 pounds pushing aginst it it'll work fine. You should still drop an airstone or something in it to keep it from stagnating if you'll be storing it for a while. Also don't store it mixed or evaporation will change the specific gravity over time.
If you're only going to be storing it for a few days you can ignore those.
I use brute 32g trash cans. You can store rodi and saltwater for alot longer than you would think. Rodi I make 15-20g last me about 2 weeks. I just scoop out a gallon per day. Salt like mentioned above if it's stores in a cool dry place you can store for awhile. BRS says mix salt for a month. Just keep a pump running I do believe here's a link