First - if you worry about it, it will be worse .
For 120, see if you can get some of the Arista/AP/Generic reels that are designed to work in Paterson tanks, but have wider flanges at the entry point. I find them easier to load then the Paterson reels.
If you have any opportunity to load in a darkened room rather than a changing bag, do so. Humidity is something to avoid if at all possible, and changing bags trap humidity. Remember that tanks can be loaded at night, labelled and then used for developing the next day.
If you must use a changing bag, do everything possible to maximize the space, "coolness" and "dryness" in the bag. Some sort of internal box or frame will help with a changing bag, even if it is something impromptu, like a milk crate.
Can you swim or ride a bicycle? If so, was it hard at first to learn, but easy now to do without thinking? Loading reels is like that.