If this is the place that I'm thinking of (47.464386, -119.873572) you could come in from the south side on a nicely graded gravel road to drop off a trailer.
The road in from the south is well graded up to just past where the BLM land starts, there is a small area that could be camped in, however we will most likely be camping more to the central/northen end. Once you get to the area with the falls, you have a choice of dropping down a very steep hill to the falls, or skirting around on another road, but that has an area with an off camber area that would not be good for taller trailers, and once past the falls there are a couple of crests in the road that could catch low hanging stuff such trailer tounges, underslug spare tires etc. Definatly not saying any one particular trailer can not make it, as some are very capable, but many are just regular travel trailers with bigger tires and labeled as off road worthy. I do not want to be responsible for recommending it, especially without knowing the individual trailer/ to vehicle combination and the drivers experience / limits. That is why I recommended the North entrance (Hiwy 2, go past Waterville, and turn south on Road H which turns into Slack Road and enters the Douglas Creek Area) and meeting up with the group after we find a camp. should be easy to find as the camping is primarily on the main road thru the area.