Custom folder selection (search) - make permanent

The great search is probably my main draw to eM Client. However, I have one small problem.

My flow involves deleting (sending to Trash) emails once I’ve acted on them. The search by default doesn’t include Trash in its results. I’ve been using the ‘Custom folder selection’ option to explicitly include it, but this option doesn’t seem to be permanent. (I’m not sure if that’s by design).

So my question is, is it possible to either:
a) have an option to include Trash by default
b) have an option to make the Custom folder selection permanent

 – I use Trash as my main store (instead of e.g. Archive) because it’s quicker to have a direct key binding to that action (the delete key). –

The Archive button doesn’t seem to work/isn’t enabled (using IMAP), or I would use that instead.