@Rusty-Any issues with storing the WTE with the end caps in place, such as the O-rings taking a set?
No issues that I know of. I believe they should be fine.
The O-rings can get a bit stuck in place so it is usually harder to remove the flange after sitting for a while.
The only suggestion that I would make is to ensure that the O-rings are lubricated. This will help them to stay pliable and not dry out etc.
I have never had a problem with my pressure proof caps that I have in my tanks that have been on for eons. The one thing that I would recommend is if the caps are in place for a while (as in months and months) is get in the habit of putting new O-rings on. They are cheap and better safe than sorry. Even if I have only used one once for a hydro run, we always change them out each time we “break” a connection. The shipyards that I deal with do the same thing … cheap insurance policy.