Short barrels and trap shooting do not really go hand in hand. Yes, you can do it, but you're not going to like it the first hundred times. Trap is the longest of the clay shooting sports, and a longer barrel helps quite a bit. If you really want something to pull double duty, I'd pick up something like a Mossy 500 or an 870 that has barrels you can swap out. Use the 18.5" when at home, and swap in the 28" for the range.
If you want to shoot a round or two of trap, let me know. I've got an O/U w/28" barrels and a Mossberg 500 w/ both an 18.5" and a 28" barrel. You can try them all out if you want. I've only shot 2 rounds with the long barreled Mossy and I did okay. I'm quite a bit better with the O/U, but it could be because I've shot it more.
