It wouldn't fit on the Zumo 350 so I stuck a Sandisk 32GB SD card in formatted FAT32 and Garmin Excess (not a typo) installed something, said the Zumo was up-to-date then dived off and installed southern Europe, leaving me with something of little value here in Beartown, particularly as the maps wouldn't unlock. Reinstalling cured the lock problem but didn't give me maps of where I live so I'm now trying MapInstall as it found the ret of Europe plus something from Freizeitecarte I downloaded out of curiosity. It will probably take all night to install this lot so I'll post back in the morning.
The Zumo had problems with the last update as well whereas my ancient Nuvi 2595, again with a 32GB card, updates without problems.