I can't speak from experience with heaters but I can speak from experience feeding a little person in the middle of the night freezing my <insert exposed body part here>, get your mind out of the gutter, I was thinking stomach!
It was actually easier feeding my older one in our old tent, where I would just roll over and scoop her out of the cot and bring her into bed. But with the camper trailer and my little man, I had to completely get out of bed, down a ladder, and almost burst into tears because I didn't have a chair to sit in, so sat on the freezing ladder with my back and stomach exposed. On the first night I think he wasn't dressed warmly enough and so woke quite a few times! Tired grumpy Mummy the next morning.
My advice would be have bubs in with you, keeps everyone warm and takes little effort to feed little one. I haven't always been comfortable sleeping with a small one, so I can understand that and you still have to deal the time they go to sleep and you going to sleep, you don't want him/her to roll off!
The other option is to make sure there is a chair set up inside, with a blanket,doona, dressing gown set up to wrap around her.
They are my 2 cents worth, I hope they help!