Your PDI list will help the most, I think. Its easy to get distracted and forget some of the systems or items during the excitement of the walk-though. I agree with Dan -
Every system needs to be demonstrated - both for your knowledge and to make sure they work as expected.
Very Important: Take your time and do not be in any kind of a hurry. The best case scenario is that everything works. More likely, something needs to be repaired. Try to have them do this right away. If too many systems are problematic, do not sign the paperwork to take possession until the items are repaired. This is important as you will have better and faster service now than at any time in the future.
A few items to pay special attention to are:
Bunks: They should open and close the bunks for you and show you how to make sure there is no canvas caught between the bunk and the seal when closed. This error is a big reason new hybrid owners get leaks in my opinion.
Bunk latches: Make sure all of the locks in the latches work and are not loose. We replaced two of these locks in the first few months because they fell out of the latches.
Water systems: They should have pressurized already to check for leaks.
Check under the sinks, near the water pump and around the water heater for leaks. We're still dealing with a slow leak under our kitchen sink. Make sure, when running the pump, that it pressurizes and then stops running and does not run again until you open a faucet. If it comes on without running the faucet, then you have a leak somewhere or possibly a shower head is not shut off.
Make sure that they do this on both city water and drawing from the FW tank and that you run all faucets, both showers and the toilet.
Make sure that they walk through how to winterize if you intend to do this come fall. Take notes. You will forget some but their lesson will come back to you at the time you need it.
Water heater: Have them demonstrate how to run off both electric and on gas. There is one switch on the heater itself and another on the panel. The heater needs water in it of course.
Fridge: The fridge controls seem to throw some for a loop. Pay attention to how to run on auto vs gas alone.
Stove: Have them actually light the stove for you. It can be touchy.
Bleeding lines: Tell them to show you how to bleed the lines through the stove top as that is useful to correct problems that can arise with the water heater, fridge and oven/stovetop.
Propane switch: Make sure you know how to switch between propane tanks as needed.
Electrical: Have them show you the breakers and fuses both within the converter under the fridge and the ones that are in line under the trailer and tongue. These cause some people difficulties if they don't know where they are and you need to know how to replace or reset as needed.
Radio: Bring a CD and/or DVD and run the radio through its paces. Make sure that the two inside and two outside speakers are working - mine still have a problem.
Jack height: Have them raise the power jack, assuming that you have one, to its highest point and then have them mark that with an indelible marker. You do not want to go over this mark.