An intriguing issue!
Just for comparison, I've found that my starter battery will also show a measurable drop in resting voltage after only 2 days or so. Surprised me that it would drop that quickly -- so far it's never failed to start the truck, but I didn't like the idea of starting with low(er) voltage, given how sensitive these thing seem to be.
I added that Trik'l charger thing to avail myself of excess voltage produced by the rooftop solar panels: after coach batteries become fully charged, the device will shunt power to the starter battery. It seems to work well, keeping the starter battery topped off.
As far as posting pics: I've found the easiest way is to click the "Go Advanced" button, and then click on the paperclip icon at the top of the working box (next to the smiley face) to attach a file. It can then import a photo from your computer, rather than needing a URL address.