One would think that any electical engineer would know how to fix such things better than I do, or at least that all are interested in fixing electrical things, but I'm pretty that not all do or are. So don't give him a hard time if he begs off. I'm sure he knows electrical engineering better than I do/
OTOH, if he will be interested, you should either have a supply of tools available somewhere or warn him before he leaves home. I keep having to buy voltmeters when I visit my brother, because I don't normally keep one in my suitcase, and more than once I"ve needed one to fix something he has. At least I could get a different model each time, and I was saving him money. I really have enough voltmeters now, so I hope I remember to take one in my suitcase, but the TSA will probably think it is a bomb.
I have doubts about sleeping with the heater. Electric heating pads warn against sleeping with the pad because, they say, you may end up lying on the pad, and indeed my mother did once and got a burn that did not heal quickly.
Not the same thing as a heater of course, but I wonder how hot the air gets and if it could set fire to the sheets and blankets.
A heating blanket is the most efficient way to stay warm when in bed. Anything made in the last 20 or 25 years has been redesigned in case there was anything to the fears about low frequency radiation. WRT high-tension lines, they finally decided it was not a problem, but I think once they redesigned electric blankets, they stopped doing research on the old ones. ??