Upgrade gets disrupted if your Bastion gets attacked and you lose. If you're not upgrading and the same happens, your Bastion gets downgraded. So, I see no difference between defending during an upgrade and just defending (unless it's at level 5, in which case it cannot get downgraded, so you don't have to defend at all).
As to "how to defend", the answer is "the best that you can". Whatever defence you pour in, you can get hit harder, especially if several BHs team up against you (which happened to my BH in the last days of Kabam... and they failed, btw). A reasonable minimum would depend on the map you're playing or, more precisely, on the strength of your enemies.
If you're a small(ish) player, only interested in reaching level 5, I suggest rubying up to that level and not wasting units at all.
hd1313 said:
Any thoughts on how to calculate troops needed to guard a bastion during an upgrade? Any suggestions on troop numbers and kinds?
Thanks
Keep on Millstone Level 5, with NO TROOPS ( you don't give any points away ) and no big Fish can profit from You. Until you get 160 good players then you can go out being a Very Bad Pirate, who ever one will want to Hunt Down.
Good Luck
Raventor