Yep, the black mud means it's totally gone.
If your trailer has bunks instead of rollers, that may support the hull enough. But, the smart thing to do would be to build some additional support onto the trailer to hold the sides of the hull.
I had talked to some guys that restored the same model boat as I'm working on and they said for my boat, it was robust enough to not need a cradle while sitting on the trailer, so I didn't build one. My boat has 5 stringers, and because I didn't build a cradle, I replaced 2 stringers first (every other one), then after those were in I tore out the last 3 and replaced them. My hull has splayed open ~1/2" at the worst since pulling the cap. I used ratchet straps to pull the hull back into shape while bedding the stringers and bulkheads, and I plan to do the same when attaching the deck. If it's still a little splayed out, I think we'll be able to muscle it back into shape when we put the cap back on.