The Tacoma should be fine if you have the towing package on it. Do you have the electric brake controller?
Do they have a clear title (no liens)?
How are the tires? How old are they as over 5 years is not especially good. Remaining tread is not a good indicator as trailer tires usually don't wear like car tires.
How about the control panel, do all the tank sending units work?
How old are the batteries?
Ask them if they have or had any leaks
Are all the owners' manuals available?
Do all the appliances work?
Is the awning in good condition?