shorter vs longer on a long trip

I see no benefit here unless you just especially WANT a smaller trailer. Remember that the chances of selling it when you return may or may not happen in a timely manner. I wouldn't mess with it. Just take your current trailer and you'll be fine.

Also remember that if you do decide to buy a smaller trailer for this trip, you're going to have license, insurance and taxes to pay and you'll not recoup this money. Not to mention the depreciation.