Sutho,
Welcome to most informative/open/ sharing Expanda forum going around. Not being familiar with this layout though pretty much off the top of my head---
open and shut everything that can and be sure the latches connect.
be sure the water mains don't leak into the van from where its connected into the offside wall,
operate all lighting/ appliances on all types of supplies (battery,electrical or gas),
get underneath it and have a good look at suspension components for damage.
inspect wiring from hitch to drums.
look at water tank surrounds for dents,
peak under the mattresses for mould condensation,also around the poptop canvas to the roof for mould,
water pump mounts are sound/solid,
jayco fitted id plates match welded markings on a frame,
gas lines arent dented,
window winders operate full action, locks work,
door lock and security door latch functional,
watch the main area and feel for movement in the ply wood,
see if the foot well has water ingress.
setec has different types of fuses (not original then why???)
sink hand pump works and has a binding pressure for suction,
service book/ warranty work performed review.
pretty much, have a visual think of the van and do a check list OR, goto the jayco website and do a virtual tour of the van and note down you want to see in detail.
Hope this helps. Pace.