It depends on what year and what type of 4wd you have in that Jeep. If it's Quadratrac II (which is likely), it will always be in 4hi. Like Slvrlng said, if it's not Quadratrac, there's no need to put it in 4wd at all, except for maybe on a slick ramp. Definitely take it out of Overdrive.
I'm assuming it has the 4.0 In-Line 6, which is great torquey little motor. That engine coupled with the 4wd suspension should be a pleasure to tow with. I used to tow my 19-6 with a V6 2wd Dakota with the mushy street suspension, and it did fine, so I'd bet your Jeep will have no problem towing the 170. One thing that you might be concerned with is that Jeeps have a relatively short wheelbase which can lead to increased swaying of your trailer while towing, especially at higher speeds. Being that the boat is a 170 and lightweight, you probably wont run into that problem, but if you do, SLOW DOWN! It can get dangerous quick. I almost lost control a 2 door Tahoe while pulling a large W/A boat at high speeds due to this swaying phenomenon. Once it starts, it's hard to stop.
Since you're going on a long trip, you'll want to make sure the hubs on your trailer are adequately greased up, and of course, check your tire pressure and check to see that your trailer lights are working correctly.
Other than that... Go slow and steady!