Thank you for the advice, everyone. It seems that the general consensus is that the setup leaves something to be desired.
We don't have many options as far as placement of the holding tank (or increasing its size), but I think the suggestion that we really try to deal with this in the fall is spot-on given that the relatively short sailing season is almost upon us.
I think we're going to take it out for now (keeping the parts), put in a portapotty, and reevaluate in the fall if necessary. The idea of removing an unused system is much more appealing than using it this season, perhaps dealing with various problems, and then having to remove it once it's been "broken in", so to speak. We could just leave the whole thing alone and rely on water bottles and a bucket in an emergency, but while I have no problem with a Lady J, a bucket may be pushing it.