I have tried feeding my BP in his enclosure and he will not eat. He only eats in him card board box, haha.

I think your process seems a little complicated, but if it works then it should be fine. Is your snakes enclosure close to the bathroom? I would just be worried about moving him a long distance right after a meal. I keep my cardboard box about 3 feet away from his enclosure so I don't have to move him very far. Sometimes I just let him crawl out of the box and back into his tub after a meal, that way there is no handling involved.