OK, so it sounds like your BP prefers to be in the cardboard box rather than the large tub. There are benefits and downsides of feeding outside the cage (many will tell you it's unnecessary - and you can feed your BP in its cage). You have discovered one of the downsides: if your snake is uncomfortable or stressed in a separate tub, it will try to escape rather than eat. Shoving things in its face or forcing it to eat may not always work, either.

In the end, you should follow whatever method produces the best feeding response. So if your snake seems to eat best in the cardboard box compared to the tub, I would continue to use the cardboard box. BPs are creatures of habit, so changing something in their routine may cause them to reject food! Try to keep things consistent.

I dip the body in hot water but I'm not sure if I'm getting the rat hot enough or what cause I have to dip it a few times before he takes it
It ALSO sounds like you may not be getting food hot enough. "A dip" isn't really long enough to heat a rat all the way through. You should be leaving it in hot water for at least a few minutes. Try the recommended method Albinos_Rule and I describe above. (You really don't need to leave a rat out overnight, just an hour or two is fine). Make sure the rat feels warm to the touch!

Again, I just want to emphasize that getting your snake to eat f/t without rejection is good and I'm glad your snake continues to eat for you!