If you can't use your 7-pin connector because you stated it blows up the truck towing fuse, how the hell do your TT service brakes and lights work when you are towing? Osmosis electrical connections have not been invented for RVs yet.
Everything you have stated adds up to BS.
He might be saying that if he tries to use the slide out with the truck hooked up, the truck's fuse blows. That would make sense since the slide motor has only the truck's power through the umbilical to operate. He has no operating battery. The draw of the motor exceeds the size of the fuse in the truck.
Trying to diagnose some of these 12 V electrical issues from a keyboard can be problematic, especially if the information given is not close to full or complete.
