I'm hoping to do some big tours this summer, but my bike can't easily fit panniers. I was thinking about a trailer. What are peoples experiences using them? Any advantages/disadvantages? Thanks for the help!

Do a search of the touring forum. Look for the word "trailer" in the title. I'll bet you get at least a half dozen threads that will more than answer your question.

This topic sparks the same sort of passionate arguments as chain lube, Brooks saddles, and single malt scotches. Personal preference is involved. One could safely say that people have happily toured the country with a trailer as well as with panniers

I use a Burley flat bed trailer on my daily commuter and absolutely love the thing. I regularly load it down with 100 lbs. of groceries or camera gear (job) and it tracks beautifully. My kick stand is almost worthless when my panniers are loaded down. The trailer works fantastically.
--A

Trailers work fine. The biggest risk is succumbing to the temptation to load them to capacity. Make a weight budget and stick to it.

The downside? The trailer is going to be a bit heavier than panniers and the racks they require. You have to carry a unique spare tube for the trailer.

I have a BOB that I use for backcountry primitive roads in Big Bend National Park every year. It works fine. If you plan to ride very steep rough roads, one disadvantage of the trailer is that the trailer weight sits behind the bike and does not help with rear wheel traction when you are trying to climb a loose rocky hill. But, if you ride on pavement, you'll never care about that.

Check out the various jackknifing/accident threads to pick up on the safety issues and how to ride safe with them.