If this was my trailer and paying someone to repack wheel bearings I would.
1. Have him check the brakes
while in there.
2. clean and pack the bearings.
3. Get a spare set of bearings and clean and pack them and put them in
plastic container and pack them in spare parts. If you have the room I
would pack them into a spare hub and store it.
4. check any plumbing lines hanging under the trailer both gas and fluids.
5. Check the frame welds and all tubing up front for cracks.
Check around the trailer steps if you have them.
6. spin the tires
and check for run-out and unusual wear patterns. check the
build dates on the tires
and fill to the proper pressure. don't forget the
7. look at the frame for rust that needs attention.
8. Spray a little lube in the working parts of the trailer hitch.
9. check the leveling jacks and spray some lube on them if necessary.
10 Check any hanging wires and tie them up.
Once you get the trailer back home check the torque on the trailer lug nuts.
it is very wise to recheck them after any service work is done and after its first short run.
This would take a few extra minutes time unless there are problems but a cursory look could save you allot of trouble later down the road. How often do people actually look under their trailers especially any retiree's.
This should take care of under the trailer.