IMHO, diligence is the key. The Norcold/Dometic fires occur when the cooling system fails. Inspect your box often. You're right there waiting for the sewer to empty, so pull the cover and look for signs of failure...usually smell of ammonia and/or yellow dust like termites are eating your cooling system. The combination of gases that cool your fridge are very corrosive. They eat away at the cooling coils from the inside.
Personally, I think the issue of fires is way overblown. Do they occur? Sure.. often, per miles driven and/or hours of use? probably miniscule. The recall from Norcold simply places another probe in the heat tube to monitor the temps. If it gets too high, the system is supposed to shut down.
From what I've been able to find, fires are much more likely to start in the engine compartment than the fridge.....Dennis