Did you tell him you'd be more comfortable staying at 40 until after your vacation? You could try calling Monday (I know he's kind of a "slow" responder and a bit spacy, but...) that could ease your conscience if he just says ok.
Also, yes, you are probably ok to taper 10mg per week at that dose and for how long you've been on it. It's when I get to the lower doses that it seems to really hit for me. But I completely agree with crohniemomx2 that you can try the taper and, if you feel problems starting, go back up by 10 mg (to 30). I bet you would be fine even at 20 for your trip. That's not a super low dose and might keep some of the side effects (moon face, sleep issues) at bay.
--40 year old female, dx as UC in '04 (1st symptoms in '03), switched to Crohn's in '05, 1 fistula, crohn's colitis, limited to large intestine
--rejected (reaction/didn't work): Asacol, AZA, 6-MP, MTX, Remicade, Humira, prednisone
--stuck on methylprednisolone, tried Prochymal in Phase III study (can't wait til it's approved!)
--started Tysabri 3/21/08
--single mom to 10-year-old girl