In reply to Roberttaylor:
If you like plenty of neighbours, Corie Raibeirt or Corie Domhain on Cairngorm reliably accumulate snow but are well known and used by groups. Though this does give the opportunity to find a ready made hole.
We've dug one out (5 man) on the side of Creggan a' Choire Etchachan near where the path up from the hutchie levels out.
Both of the above definately accessibly by train, bus and walking.
look for scoops and bowls high up, cairngorms do tend to be good for them and pretty reliable (for Scotland!!).
I'd avoid anything like gullies as potential for avalanch or suddenly and unexpectedly finding yourslef joined by skiers, walkers etc is much higher!!
Cheers,
Stuart