I'll be picking up a new to me 2004 FW here in about two weeks. I'll be towing it back about 500 miles from PA to IN. What should I do/look for when I pick it up? It sits on a dual axle Four Winns trailer.

If you haven't done it already, get on your knees infront of each wheel. Put you bear-like grip around each tire and shake it, back and forth, as hard as you can. Fix any excessive side-to-side slop before your trip.

Probably want to have a pro look at the trailer hubs, bearings, grease fittings, brakes, and especially tire condition before you get there. You'll want appropriate jacks, blocks, tire irons, flares and spares for both the trailer and your tow vehicle "just in case". Nothing worse than having to spend time on the side of the road on a long haul, with the single exception of having to leave your tow on the side all alone while your off trying to find any of the above. Don't know about your old SeaRay, but the FW probably uses the 'flat 4' connector, and surge brakes. Nice thing is your Durango should pull that Sundowner along like it wasn't there.

Check the tire pressure! The single most common cause of tire failure is improper inflation. Does it have a spare? Buy one if it doesn't have one.

All of the above, plus recheck the trailer tires nut torque after the first 50 miles and touch the center of the wheels (hubs), at each gas stop, looking after bearings overheating.
good trip

An oldie but a goodie

Road Trip Check List

My trailer is a FW 2004 with surge brakes, and I have a 'flat 5'
Make sure you ask ahead of time so you can get the proper adapter and/or wiring in place. Without the 5 pin you will never be able to back up. In a pinch however if your trailer is like mine with the removable tongue (not the swing away) there is a quick disconnect in the brake line so you can remove the tongue. Just remember to rehook it before you drive. Also check you mater cylinder for brake fluid.

You can plug a flat 4 trailer plug into a flat 5 connector on your vehicle. So, you can make sure your vehicle has a flat 5 and be sure it will work for both.

Connector issues are none, I've discussed that with the seller. It has disc brakes.

If it has disc brakes, it would have a reverse bypass solenoid on the hydraulic line, or a manual lockout. the bypass solenoid is typically where the 5th plug point comes from. The solenoids are notorious for failing. If it fails, you can't go backwards. Make accomodations for a make shift manual lock out just in case.

Take grease with you for the trailer bearings, and as others stated, be sure to have a spare.

As been previously stated check the tire pressures. Add a few whacks of grease into each hub and you should be good to go.

What WM said! My FW trailer has the flat 5 with the reverse lockout. If the solenoid fails or isn't working, you can insert the hitch pin into the manual lockout holes in the coupler. I think these are standard on all FW trailers with disc brakes since at least 2001 (a friend has a 2001 FW with the same setup, so I'm assuming here...) I don't have a picture of the coupler and pin, but maybe someone else does??

Now, with regard to my Fountain Lightning and 50' Post trailers.... (oops, wrong thread)

Small piece of plywood as a "foundation" for a jack if you have to do a change in sandy or muddy shoulder. I also have a length of pipe in the trunk to slip over the tire iron. The extra leverage turns this weakling into the hulk

Safety chain from bow eye to trailer stanchion (don't rely on the winch strap).

Check rear tie-downs.

I'd bring a small toolbox with some misc. hand tools. Also, some duct tape in case the canvas wants to come loose during the trip.
When I brought my Chap back from Fargo ND.(800 miles one way) I had the dealer shrink wrap it after I checked it out, cost about $200 but it was nice knowing it was protected from road rash and weather, and I didn't have to worry about canvas flying off.

As everyone has already said, bearings and tires are your biggest concern.