This is about the best links I found for Bolles Harbor. The DNR site is useless, do a search for boat launch and you can't even get a list. I spoke to the gal at the contact number for Bolles she did not know about overnight parking. She said a man was coming in later that would call me. Bolles is easy to get to and very close to the LasPlasisant exit off of I 75, it really is a good place to launch and they have over 300 parking spaces, so not being able to leave a trailer is ridiculous. I argued with them last year and got no where, they said that they have to make the rules the same for all DNR ramps not matter how large or small. I don't think that rule has changed but I am just wondering and a little worried what the consequences are if you do it anyway. I will investigate more since we want to use it tomorrow, and let you know.
What part of Detroit will you be driving from, if you mean you are going to be by the Detroit Metro Airport, then Erie Metro Park would not be a bad drive, and it is definately better to keep your rig there.