I suspect that the solution might depend on the project, rather than necessarily being defined by your GTD system.
I was thinking, "I don't record Done actions," and then I realized that my Bed Book, mentioned a couple of times in recent threads, is pretty much exactly that. It's a bound notebook with one page for each of my 120 garden beds, and when I do something meaningful to a bed, or notice something about a bed that I want to remember, I note what I've done in that bed's page. Since "do something" is often a result of an action, that means that it's effectively a record of Done actions.
Generalized, it's essentially a lab notebook, which is one classic way of keeping a record of done actions--though, again, it's probably not thought of precisely that way. I think that a lab notebook or binder could be useful for a lot of different projects. I'm not imagining sitting down to do a lot of writing at the end of the project, but instead keeping it as a companion through the project.
Other random examples:
When writing code, changes are often recorded through comments, test records, release notes, etc.
Meetings get meeting notes. Or the lab notebook could be used for taking notes.
In general, I guess I'm seeing the problem not as "recording done items" but as keeping a record of potentially useful items, throughout the project.