Thank you for rescuing this kitty!
...and Welcome to TCS!
We absolutely know this routine - it's just our Tasmanian Devil was only an 8 week old kitten, so he wasn't able to levitate the crate - so the door didn't open and he didn't escape. But he got pretty well scratched up - as this kitty will when trapped. Do your best not to let it freak you out. It's like making a child take medicine they hate - you have to do it for their own good, even if they don't understand it yet.
for local rescues. At least one of them will rent or lend a trap. (Often it's just a security deposit you get back when you return the trap). Or google "cat rescue in XXXXX county," or "cat rescue in City, State." You'll find one.
When you get the trap home, wash it with a very light bleach solution - get the smell of fear and other cats off of it. Since you're planning to transition him to an indoor kitty anyway, buy Feliway spray. This is a synthetic hormone that mimics the "friendly" markers in cats' cheeks and helps reduce stress. Spray the wires of the trap on both ends with the Feliway.
Feed him in the trap WITHOUT SETTING IT TO TRIP. I normally recommend that dirt be poured over the bottom of the trap - this way the cat doesn't have to walk on the wires and the trap just lifts right up through it... but being that it's on your deck, try laying some newspaper over it. He'll still trip the trap when it's time.
Once he's eating in there (don't worry if he doesn't the first time. Cats have long memories, and he may be wary of the enclosure after the last incident. Let him go hungry - he'll just be that much more willing to give it a go the next day) for a couple of days and you're ready to get him to the vet - set the trap.
Now - have your car ready. He's going to be FREAKING OUT based on what happened before. The car ride may result in him peeing, pooping or vomiting (or all three) out of fear. So have wherever you are going to place the crate covered in a plastic tarp you can toss. We always covered the trap in a light blanket, leaving the ends open. And we opened the front windows a crack, so there is fresh air, but not a lot of air movement.
Don't worry so much about the trip home - he should be fine in a crate. They're usually VERY happy to be leaving the vet.
Since you're going to be bringing him inside, maybe go ahead and purchase this CD: http://www.musicmypet.com
Maybe consider playing it on the car ride to the vet - harp music REALLY helps scared cats calm down. And talk to him as gently as you can - explain that you're just getting him fixed up so he can live inside with you and be a spoiled kitty, warm and dry for the rest of his life.
For when you bring him home.... have a "safe" room ready for him. Cats are all about territory - and his is about to change. You're ahead of the game because he's friendly to you now... but he may become scared again when you release him into a room, not onto "his" deck. Have the room already sprayed with Feliway, have water and food and his litter box(es) set up (cats that have been going outside often prefer not to poop and pee in the same box, even if scooped). But make sure he has a hidey place - a box on its side, a table with a cloth over it that hangs almost all the way down to the floor... something.
When switching territories on a cat, it's easiest on them if you give them a small territory first - thus just one room that has a door. Give him a few days to make that room "his," and to get used to all the new scents, sounds, &etc. Play it by ear after that. If he's really scared, we've got more tips for you.
Just didn't want you to expect that he'd be happy at first being brought in - it can take them a little while to figure out that "hey - this is a good thing!" They have to get over the fear of the change that just happened first.