Brompheniramine causes significant sedation and drowsiness, which is going to put a damper on your enjoyment of the trip, even if you don't take enough for it to actually cause a deliriant effect... and it's not like the dry mouth (and other side-effects of non-deliriant doses of anticholinergics) is particularly pleasant either.
Also, brompheniramine inhibits the re-uptake of serotonin to some extent; the first SSRI, zimelidine (which actually predates prozac, but was withdrawn from the market after a few years and is thus mostly forgotten) was developed from brompheniramine. Not only that, but the brompheniramine is probably going to compete with the DXM for your liver enzymes.