Gator and RJP -- you need to read the whole post, not just part of it. There are two different things being said -- both, I believe, are true:
1. IF the plan is to go on to Full Cave, it would be better to do Cavern in doubles -- that is one part.
The other part:
2. To get the most out of Cavern, do ALL the OW stuff in Open Water BEFORE you take Cavern or any other overhead class.
In other words, the best thing for the OP to do would be to switch over to doubles now, get familiar with the rig he would be using in the overhead and THEN take Cavern -- but that doesn't sound like that is what he will be doing.
OR do both of you think there is no additional advantage in taking Cavern in doubles at all? That you would learn just as much, and be prepared to go on to Intro/Full, if you took Cavern in a single tank and then later learned how to dive the gear you must use for Intro/Full?
Knowing Dennis, I am quite sure that was his intent.