Hot glue to hold rackpack?

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I've bought a new pack that slots over the rack on my roadie, however the straps are incorrectly aligned and they are almost useless as a result.

My rack is basically a Torpedo7 seatpost rack ~ a large flat plastic bit that you can put the pack over. My question is, would hot glue gun stuff be suitable to hold it in place since I can't use the straps? Or will it melt the pack?

PS The yellow strap fell apart on the first ride.