Jason, I know it's not an immediate concern for your own little guy yet (maybe for other visiting children though), but having a sump next to your display, at or below eye level for a toddler, with no cover on it can also be a recipe for a HUGE tragedy. Pennies, toys, unwanted hands are just minor in comparison to the potential for disaster with the possibility of a child falling into the sump head first.
Placing the sump underneath your display can allay ALL the above concerns. If you can possibly manage the relocation of the sump, I think you'd be doing yourself a great service and allow you peace of mind.
Also, placing a lid or cover on the sump will just be another place for heat to build up.
JMO, and I'm off my soapbox now.
Russ