Stray+Carrier

hi guys, seeking advice.

we recently found a stray cat, he's probably around a year old. we want to take him to the vet but he is absolutely refuses the carrier. he will get in, he will even sleep in there but the second the door closes he absolutely loses it. he gets super stressed, tries to get out and if we don't open him up again he might hurt himself. we've tried to leave treats, tried to make it as comfy as possible, put his favorite blanket in there, but to no avail. this dude needs to get his shots and get checked out but so far we can't get him to chill.

any tips would be super welcome.