i have some 2-piece whistles that are made of plastics (e.g., dixons, susatos). when i am not playing them, is it important to separate the head from the body while “storing” these whistles? i am planning to make a whistle roll (not unlike the one emmline recently posted about) to store all of my whistles in one “case” instead of having each one in its own separate pouch. the roll will be easier to make if it is okay to leave them together in one piece, and store them in the whistle roll that way. are there reasons that i shouldn’t do this? will the joint suffer any ill effects? (maybe this is a silly question, but i am used to a boehm style flute that has to be broken down to fit inside the case, so it’s never been an issue before.) thanks for any info you can pass on!
There’s no need at all to separate them, especially if you have a safe place to store them.
its the multiple piece metal ones you need to worry about: corrosion could set in and weld the pieces together. (Especially if the metal is different kinds… I think…)
The plastic ones don’t matter, becuase plastic is sort of its ow lubricant. (Can be…)
If they were high end whistles I would offer to store them a my place, no contract of monthly administration fees. 
MarkB
On wooden whistles (and flutes) it’s good to store them disassembled so that the tenons don’t warp or compress over time due to the pressure of the joint.
As noted, metal joints can freeze due to dirt or corrosion, so it’s a good idea to store them separated as well…and if it’s going into long-term storage, couldn’t hurt to coat the assembly points with a good coat of cork grease as well to help keep moisture off.
Neither apply to plastic whistles, unless like the big low Susatos, they have O-rings. These should go into long-term storage disassembed, so that the O-ring doesn’t freeze the joint together over time.
–James