I just let mine run around like slightly insane, mostly small people. That tends to tucker them out well enough.
Also, when not camping, they have a good routine of up at 0600 and to bed my 1930, so sleep tends to come earlier rather than later with them.
My kids have the exact same rigid routine at home. They also have all the opportunity to run around at camp. They still don't fall asleep easily. We had a bit of trouble with my boy when he was younger, but he's pretty good now. But my daughter is really difficult to get to sleep at ~20 months. It's just too exciting for her to be in this strange place lying down next to Mom. She sleeps well at home, and has been in a real twin size bed since she was ~16 months (due to a penchant for climbing out of her crib) but the tent is just too exciting.
All kids are different. And the only thing worse than kids who won't sleep is parents who judge other parents based on the experiences with their own kids. All kids are different. That's why nobody has written a definitive owners manual for them.
FYI, Dramamine 1 is essentially the same drug as Benedryl but also contains Theophylline, a stimulant like caffeine. Dramamine 2 is a different drug altogether, meclizine, and causes even less drowsyness. I'd even question the point of using it. Just use a half-dose or even less of Benadryl.
Dramamine 1 also takes much longer to take effect, up to 4 hours, and then lasts longer, could still be in effect the next day. Not really what you want if you've been struggling to get them to sleep drug-free until 2AM.