I listened to a podcast recently and it was probably one of the beersmith podcasts, they were discussing dark beers and mentioned that one of the problems making malty, chocolatey Porter and stout is that those grains are counterintuitive. We think of the light chocolate as light tasting and the dark chocolate malt as something that's going to be more overpowering, and that's actually the opposite of the truth. The light chocolate malts are far more harsh and not nearly as smooth as the much darker roasted versions.
I have not tried to do this yet but it's on my list of goals. I think when I do it I'm going to avoid the two row and pale malt which is what I would typically use, and use either Vienna or Munich as the base malt. And almost certainly a domestic Vienna or Munich because they are much more pronounced than the overseas counterparts. But that's just me thinking aloud and I know nothing about this. LOL. Like Denny says, think of the recipe in your head first. Well, I have a great idea in my head of what I think it should be. I just have no idea how to get there.
Funny you mentioned about staying away from the caramel malt. I recently made two batches of lager on the same day, and one of them I ended up throwing in a pound of 10 L because I needed a pound of grain to make the the grist weight equal and it was sitting here. The batch with the 10l is Head and Shoulders above the other batch. I just had people at the house yesterday unanimously confirming that.