Seven hours is a long time to be pulling a trailer that you don't
know is in good condition. Please be careful!
If
- the tires are more than 5 years old
- there are cracks in the sidewall
- there are cracks between the tread and the sidewall
Then replace the tires. Don't take a chance on them. A blown tire at best is a dangerous delay, at worst it can cause total loss of the towed vehicle and possibly the towing vehicle (or others behind you). Two (or four) new tires are cheap considering the potential loss if one or more fail.
If the hubs have not been serviced in the last year, service them before you put the trailer on the road.
If the hubs have not been serviced in more than a year consider replacing them.
Jack up each wheel and spin the tire. If there is any rumbling or squeaking, if there is any resistance, if the wheel does not spin freely then replace the hubs.
Don't forget to check the suspension on the trailer. Springs, hangers, and axles along with the associated hardware all eventually need to be replaced. Make sure they are up to the trip.
Once you hook that trailer to your vehicle you are legally and morally responsible for what it does.