multiple UTM zones

[Bill Goran]

When working with a region in two UTM zones (if you want to stay with
UTM as your coordinate base) try extending one zone to
cover the entire region.  This works best if one zone dominates your
region - and you're only extending partially into the neighboring zone.
The Defense Mapping Agency uses this approach when they create "special"
maps covering an entire military installation that straddles two zones.