Be as anal as you want, it's your rig, and it's better to catch anything that doesn't work correctly before you drive away. You may want to take a video camera, to use as a refresher if you forget something. Take your significant other as well to the PDI, it's best to have two heads remembering things than one.
There are not as many ElkRidge owners that frequent the forum, but hopefully someone will chime in with a recent experience.
Our PDI was pretty rushed due to close to closing time, and a bad storm hitting at the same time.... we had TT experience, so we mainly focused on what was different with a 5ver.
From what I've seen from others posting of their PDI experiences, be sure to check behind the basement wall for leaks.... on our rig there was a 2x2 covered opening to let you get to the pump and winterizing valves (since they were not in the UDC, like the bigger 5vers). Make sure the furnace and AC work appropriately, check that there is adequate air coming out at the right temp of each vent.
Make sure slides go in and out smoothly multiple times. Check that the seals are working as they should (flipping out as the slide moves out). Make sure they show you how to hitch and unhitch, and then let you do it, yourself. (we didn't get enough info on this!)
I believe there is a checklist on the forum that may help also.
Erika