Why has our new kitten started hissing after two weeks?

My husband found a 8-10 week old kitten in his boat a couple of weeks ago. He brought it home and so far it has done pretty good. He eats, drinks and uses the litter box. We have taken him to the vet and he seems very healthy. We have given him his own space in the laundry room where he spends most of his time behind the dryer. However, my daughters can get him out and play with him for long lengths of time without a problem. He will sit on all of us and purr and snuggle, but the second you put him down he darts under the couch or behind the dryer again. We try to give him his space when he does this. Anyway, I thought we were making some progress with him, but then my daughters went out of town for a couple of days and now all he does is hiss at me when I look at him over the dryer. What's up with that??? He hasn't done much hissing before. My husband was finally able to get him out from behind the dryer last night and coaxed him to let us hold him. Once we had him, he snuggled right up and purred for an hour. I don't know what to do!!! I can't have a kitten that starts spazzing out on us the longer he's here. I realize he's scared, but shouldn't he be coming around??? I don't want my kids to get any more attached to him and I don't want to spend any more on vet bills if we aren't going to keep him...which we won't if he can't be nice. HELP!