There's a PLoS One paper where ChIP was performed on RNALater-preserved tissue (Article Chromatin immunoprecipitation (ChIP) method for non-model fr...
) and since it is advertised as a preserving agent for DNA and proteins as well (https://www.researchgate.net/post/Western-blots-on-tissue-which-have-been-stored-in-RNAlater) I think it might work if your samples aren't too old