I don't have a definitive guide, but I'd suggest looking at these videos if you haven't already:

* [Retr0bright - de-yellowing do's, dont's, and playing devil's advocate](https://www.youtube.com/watch?v=xBS_UEV35W4) by Modern Classic
* [Hydrogen Retrobright Experiment](https://www.youtube.com/watch?v=pFFDSHDtVNg) by Chuck Hutchins
* [New Retrobrite Technique for Indoors | Sous Vide and other methods to reverse yellow plastic](https://www.youtube.com/watch?v=05RSh3d-EuA) by RMC - The Cave

The last one seems like probably the best solution for countering the risk of marbling.

While I haven't watched it yet (I'll update this once I do), [The truth about Retr0brite – busting myths with science…](https://www.youtube.com/watch?v=YPl356YKcVs) also showed up in my sidebar and tech YouTubers who I *do* follow have left favourable comments.