Ours is stored indoors in a large building on a chicken farm. On the face of it that does not sound like a good idea however we have been there 10 years & never a problem.
I suspect that the farm runs a very effective rodent control program. No feed kept in this building. It is for equipment storage & a workshop. We also do the dryer sheet & liberal use of mothballs inside & all is closed up for a 6 month stretch each year. We open up in April & the odour of mothballs is still there. Must be enough to keep the rodents out.
If leaving the unit unattended setting out traps or poison inside do not seem like a good idea to me. Hate to think what the smell of dead critter will be like after a few months.