Don't leave either gray or black valves open - dump tanks when needed. You will get black flies sooner or later if you do.
Make sure you have working smoke and carbon monoxide detectors - schedule tests and have spare batteries.
With the exception of the factory furnace, don't use a heater with a combustible fuel for heat in the winter - no mater how many windows you leave open.
Checking for available park models is a great idea. But if not, look for a TT with at least one slide out for more room - makes a difference for long stays.
Upgrade the mattress - especially if used.
Run the water heater on electric only to conserve propane.
Check the tires on a used TT. Look at the date codes. Old tires are a great bargaining chip.
Keep the tires covered while parked.
Good luck!