What's the (specified) float current of the HC800? (I couldn't find any spec).
The SunGuard 4.5A controller has a standby current of 6mA.
Certainly with a 10W load alone, a mere 800mA will cause a drop to the battery voltage and begin its discharge.
And IMO, for a full-time 10W drain, 30W of panel is not enough.
I usually at least quadruple the load power - unless perhaps good tracking and clean sun power is available, then trebling may be ok except near & between the darkening solstices.