As long as you have got your husbandry correct, once he is comfortable in his enclosure he will probably lighten up a Lil .... As far as your feeding/prep method this time, sounds good ..... If you "scent" his enclosure or the room he is in, it will put him into feeding mode .... I usually thaw my feeders out and then once they are thawed/room temp, I then move them to the snake room and let them sit on a heat mat with a heat lamp on them and usually after 15 to 20 min they are about 100℉ and then I feed everyone .... By warming the feeder up in the room with the snake you are scenting the room up and when your snake smells it they go into feed mode .... By the time I open the tub to present them with the feeder they are already waiting for it and I'm lucky to get the feeder all the way in the tub before they snatch it ..... So yes your last used method with using the heat gun in the room your snake is in will be your best bet, I think you'll find it only gets easier from here