Hi Ian,
I observe Eta Carina regularly both through the scope and binos and naked eye. It sounds to me like high cloud could have been the problem- what looks like a nice clear night sometimes isn't necessarily so. On a good night along with some observing experience (I'm assuming you're new to the hobby?) you will see some great features, dark lanes etc. The moon as well will degrade the nebulosity. I assume you're observing without any house lights, street lights around you and if you wait for your eyes to get dark adapted (20mins) you will see much more. Averted vision as mentioned before, also greatly helps. Each night will provide a different view depending on the sky conditions, and those special nights when it puts on an amazing show, you will just about fall off your seat.
This is easily visible to the naked eye even with light pollution (not so sure if you view it from say the city, but I only live 15 mins away from the city and I see it easily. Allow your eyes to dark adapt- 10 mins minimum and use averted vision (looking just off set from it and it's large size and nebulosity should be very apparent.
To gauge the sky conditions for that area, I use the Omega Centauri globular cluster- if I have trouble seeing it naked eye, then I know not to expect to see too much in the way of faint fuzzies.
I'm glad you found in the binos - it puts on a great show in binos
- low mag. the key. But throw on some high mag to get into the homunculus nebula and the keyhole!
Here's a guide to help you gauge seeing & transparency.
You haven't yet answered anyone's questions whether you're new to this hobby or not, so I've posted with the assumption that you are a new to it.
