I have a 28 ft. TT and had the wheels bearings completely serviced in 2019. I have used the trailer only twice since then for 2 trips of 400 miles total. I would like to make another trip of about eq...
I would pull one hub, check bearings for proper amount of grease, and look for any sign of rust or contaminates. If one is good, likely all are good, as done at same time, by same person.
You shouldn't need to pull the seal on rear bearing, just look closely, with good lighting. Looks good...reinstall, take your trip.
If you had done a complete bearing service yourself, knowing that the job was completed properly, then I'd just go on the trip, not worry about it.