Ive always had classic minis and a few NEW minis too, check all the usual places for rust - round the headlights, sills, floor panels, battery box (in the boot).
In fact this http://reviews.ebay.co.uk/Mini-Buying-and-owning-a-classic-icon_W0QQugidZ10000000008460604 guide pretty much covers all the points I was going to cover!
Parts are plentiful and reasonably cheap, car is easy to work on and everyone loves a mini
Good luck , any more questions PM me
Are you getting the trailer too?? Is it a P&L conversion?? They used to make those trailers and do fancy paintwork. Check their site out http://www.plmini.com/stlt.htm