Free 1996 35’ Gulfstream Innsbrook.. worth it?

Honestly, if you're willing to put that amount of time in and have the skills you're much better off building from scratch. Perhaps take the trailer and grab the AC, heater, and fridge if it works and build your own from the frame up. You'll send up with a trailer that's superior to basically anything you can buy (and certainly better than having up a rotted out old trailer) for not a lot more money.