@Zephyn.
Much as I hate to be the one to tell you this (but which should be obvious):
If you're concerned about security generally or the contents of PM's etc. then you you shouldn't be posting and sending PM's anywhere on the Internet. Let alone on a site such as this. And that includes emails. This in spite of any encryption methods being used. As long as there is an Internet connection involved: you're vulnerable. It doesn't get much simpler than that. The only question is just how difficult you wish to make it for somebody e.g. law enforcement to be able to read your messages and how much they're prepared to invest, both in time and in money, in order to achieve the same.
People seem to put a whole lot of faith into encryption. And that's misguided. It doesn't matter what encryption method is used: bear in mind that the message has to be decrypted in order for it to be intelligible to the recipient. And right there is where it falls down (for most all but THE most security conscious). Not that it's an easy endeavor for interested parties. But if all else fails: there's the failure point of last resort.
The above not just applicable to PM's or emails by the way i.e. documents etc. too.
VPN's? If you're that important to law enforcement: the only thing they're good for are fooling Netflix or YouTube or your other average Internet user or stalker (type of thing). Some may be better than others. But none are infallible.
Tails? Not privacy, encryption of stored data, or destruction or obfuscation of evidence that I'd stake my life on. Not unless you're prepared to physically destroy pieces of hardware after each and every session. And even then: note some of the above i.e. by that stage it could be too late anyway.
I'm not trying to put the fear of God into you or anyone else. And you'd have to have a very big target on your back and be a person of major interest to law enforcement in order for most of the above to be of concern. But don't be fooled into thinking that the better the technology, and the more in use, the more secure you are.
If it's just this site or forums generally: let's assume that somehow somebody does just happen to get a hold of your login details. Then? Worst case scenario they have access to your email address used to register (and which should be a throwaway email address) (but even that's an exercise in futility I assure you) and your PM's here.
With regards to PM's: well then you have to question the actual content of your PM's i.e. always be playing Devil's advocate when sending PM's. In other words: what would happen if the PM I'm about to send were to be made public or fall into the wrong or unintended hands i.e. would there be any adverse consequences or ramifications. If the answer is yes: then don't send it (matter of fact don't even start typing it).
Posts: they're public. No need to even comment on that.
Deleted threads, posts, and PM's, and not to mention drafts: this topic has already been adequately covered before.
Toning it down a bit though: for sure if you're worried about some personal or potentially embarrassing content being made public or read by staff or accessed by somebody who may have obtained your login details on this site then by all means use some sort of encryption. Matter of fact simple obfuscation would probably suffice. Unless I'm grossly out of touch with reality: I cannot see anybody here, that may have access to your PM's, having the time on their hands nor the inclination to go trying to decrypt or decipher a PM that may or may not contain some little bit of juicy gossip.