After reading all the comments, I have learned (& a little more confused)
about caching workunits. I think that from now on I will send/receive
workunits 2 times per week.

I have decided against letting my pc's to run unsupervised for the 3 1/2
weeks that I will be away. I want to come home to 2 working pc's.
Instead I will go for the 'friends to look after' option. One of them is now
looking forward to having another pc so he can LAN game at home & my father
will look after my other pc.

Thanks to all who replied

Brian
3888 units