I would:
- Read the manual cover to cover
- Put it on jack stands
- Remove repack inspect the bearings; most manuals say 12 months or 12,000 miles, whichever comes first
- Inspect brake shoes, magnets, moving brake parts
- Reinstall, adjust brakes
- Check tire dates, replace as necessary
- Make sure you have jack and lug wrench that works with trailer lugs
- Check the spare tire
- Check interior/exterior lights
- Get extra bulbs for interior/exterior lights
- Service the fridge/water heater/heater. Clean vents, check for bug nests etc
- Make sure propane tanks are full
- Spray with water, make sure no leaks at windows, vents, AC, antenea
- Service the water system
- bleach the tanks, flush
- replace water filter
- make sure you have water regulator for city water
- make sure you have all the fresh water hoses and fittings you need
- make sure you have all the waste water hoses/fittings you need
- spare fuses for the electrical
- Remove and check the batteries
- clean all connections
- check electrolyte level
- Get a broom/dust pan
- get a mat for dirty boots etc to set outside door
- Make sure your brake control is readjusted properly if needed
- Have some extra blocks, chocks etc to set under your jacks when parked in dirt, and to help level
- I added lights to help backing; if we head out Friday after work, it is often dark when we get to camp site