Thanks for explaining this. Why do Dr's. make things so hard to understand. Sounds like you really have things under control and are feeling good.
Cytomel is a fast acting drug with a short "half-life" in your system (just hours). Synthroid (T4) takes weeks to build up the dosage in your system and weeks to come off of. If you go the Synthroid route, it will take you a much longer time to get "hypo" for the RAI when you do eventually do it. I would put off your trip, do the RAI, and be done with it, if possible or do the RAI sooner.
That being said though, you can go onto Cytomel for extended periods with no real side effects if you're not sensitive to it. I was on it for almost two months before getting my RAI. They wanted me to do it sooner. I just wanted to put off the RAI for a while and "be a normal mom" around my house before launching into yet more "sick mommy" time.
You may also want to mention the Thyrogen shot to your doc and see what the response is there. I had to go hypo the old fashioned way for my first, of what I suppose will be multiple RAI's. My doc felt that the shot didn't work as well the on the first round of RAI to kill any remaining cancer cells, but, more and more docs are doing it the first time around! Just my luck I had the old-fashioned one!
Keep us updated! Good luck.