can you slide the building back a tad? the loco should have overhang, of an inch or two, before the wheels come to rail end. Careful placement of the yellow track stops might just allow you to have slightly more room to exit without more track length. (from the photo it appears this might be possible....not sure about the curve behind the shed and any car and loco overhang and hitting the rear of the shed.
I have built both of mine full length, because.....while not as visually interesting, its far more functional. the short shed...useless for all but a stainz , otto, rail truck. FRR loco, I imagine (don't know first hand if a stainz will actually fit.)
I have occasionally left locos in the sheds, over night, to protect from the somewhat rare light evening summer rains we get in Denver. As much as to protect from splatter of soil as water. Spiders will eventually take up residence in the shed unless its routinely hosed out and cleaned.
But like others, even though we've had zero issues, I take my things in almost religiously, just because id be so upset if something were taken or vandalized....kids can be brazen.....and....our Mastiffs sleep inside.....
I think I am going to be OK . I haven't got the kit yet but I have the three way point I was waiting for, made a cardboard floor space template, and with a bit of realignment of the track leading up to the area, it seems to be just about OK. Glad I had some bits and pieces of short straights to help eek out some precious mms.