hello,
what you can try to do is every time you approach him with clothing or collar, have plenty of treats with you and give him treats for being near the clothes and investigating the clothes/collar. and let him play with the cloths if he wants to. this way he will associate clothes with good things. and he should eventually love to be clothed. you have to be patient with him though, because if you rush it, then it won't work. he will continue to dislike it.
good luck!
