I would add that while the conventional wisdom is that the dollar will continue to fall, "conventional wisdom" has been wrong before. In fact, a lot of academics have gotten tenure on expectations theory, which would suggest that the visible economic conditions that lead to a weak dollar are already "priced in". Beware of forecasters who use hindsight to try and prove their skill. There's the joke about the guy whose clock is right twice a day, or the guy who successfully predicted 17 of the last 3 recessions.
On the flip side, a forecaster I trust - Warren Buffett - has been playing the currency markets, having made a big bet on the decline in the dollar. But I'm not sure, he might have unwound that trade.
Regardless, it sounds like a lot of hassle, transaction costs and risk to try and hedge a vacation.
Caveat emptor.