Ours are silent at the moment, but a waterproof grease might work well. Just be sure that you wipe any excess with a rag so you don't get it on anything (like you!) in the event of contact with the hinge.
I've used white lithium spray grease in other, similar applications and it works quite well. It can be found in most automotive stores, or a hardware store if you still have one in your town. I suspect that the big box stores also would have this type of lubricant.
1975 Westfalia (VW)
2014 Rockwood A122