here's how I did it:
Note the temporary basement floor support:
If the boat has ablative bottom paint, you can just rough it up and add more ablative (wear a respirator/goggles it's very toxic)... if you are looking to painting the first time (gelcoat only) make sure to rough it up and then put barrier coat on.
If you already have ablative on the bottom and you want to redo it, I strongly recommend PAYING someone to soda blast first. Second if you insist on doing it yourself, use a scraper, then lots of sandpaper, respirator, monkey suit, goggles.. a must... also the dust is toxic, sweep up in the same gear (use approved disposal).
Ok topsides are below the deck, and above the waterline... rough up the gelcoat, then paint with awlgrip, pettit, or interlux brightsides... BUT if you only have a dull gelcoat, consider instead, 600 grit wetsand, compound/polish/wax (it'll look stellar)... but if because you have huge dings, and you have to fill, then painting is your only option, then check out the paints.
I gave you this "crash list" because I am doing all this right now. Not a "weekend" project even on a 19 footer. Several weekends sure.
PS: don't bother with a cradle... if you have bunks (not stands - I have stands), jack up the trailer on one side... tilting boat/trailer Tie the boat off pulling it to say starboard (jacking up port) this will flop the boat to starboard... drop the port bunk... paint, then wait for dry time... then put the bunk back and repeat on the other side. I did my Capri 22 in 2 weekends doing this. The boat will rest on it's keel/swing keel mostly, and flopped to starboard it'll be plenty safe (tied off to starboard). Pictures worth 1000 words here:
and here (note I had a wing keel, so I could literally just jack up under the keel, and raise the boat off the trailer).