Thank you all for responding! Yeah, trust me, he has heard about all the benefits of having a feeding tube from both my mom and I and all his doctors. He's not doing it. He said he is like my daughter (who is 3), stubborn and hard headed. Haha. He is fully aware that if he doesn't keep slamming down those shakes and drinking enough water be could easily end up in the hospital. He is bound and determined to make it. He is not a complainer. He would have to be near death before he complains about being in pain. He'll just say it's "uncomfortable."
Anyways, nobody can force him to get a feeding tube. All I can do is support his decision and come to you all for ideas on things for him to eat/drink.

Also, what is considered a "round of chemo?" My dad goes for his chemo once a week (his doc said he is actually getting a pretty mild type). Doc also said when his radiation is done, his chemo is done, which is April 25th. Also, so far, all his blood work has been good.