Alice Packs with frames are good up to about 50 pounds (they will hold much more, but become uncomfortable). I find them very comfortable myself. I think being taller has something to do with it, as it hits my back in a comfortable spot. A lot of people do complain about them tough. I am uncertain about the "two slots" but I think you are talking about where most people tuck the whip radio antenna if they had a large radio to carry.
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