Originally Posted by jhohe
Any and all advice is welcome.
There are some beautiful non-reservable campgrounds like Slough Creek and Pebble Creek that would accommodate a 25 foot trailer. On the outskirts of the northeast entrance there are some great Forest Service campgrounds as well. My favorite is Soda Butte Campground (where the grizzly attack occurred this year).
In mid-June you'd probably be able to find a site without a reservation. You won't find a serene and peaceful park, but there still won't be the mobs of people that you find in July and August.
Unless you are highly experienced with mountain towing, I'd avoid towing through the Beartooth to the northeast entrance. I've seen big diesels with horse trailers up there so I know it's possible, but those are some steep and winding roads. You might even end up on snow covered roads in mid-June so watch the weather. I'd recommend coming through Cody, parking the trailer and then driving up into the Beartooth. It's a beautiful drive.