A better solution would be to use a dry duffle. Get the kind with shoulder straps. Then you can carry it as a pack on dry land, or tow it behind you in the water, as you suggest. Loaded appropriately, they will easily float. (As long as you don't try to load it with 10,000 rounds of ammo. ) In a pinch they might even work as emergency floatation if you accidently step into deeper water.

The SealLine website gives an idea of the range of options available. (Usual disclaimer. No affiliation.... yada yada.) There are other good manufacturers as well.

We have a bunch of these things in various sizes. Small ones that will fit in the hatches of our sea kayaks, as well as big ones that we've used on raft trips. We also use them when traveling coastal areas by water taxi or when flying in via float planes. That way if someone fumbles a bag into the water when unloading on a beach, your stuff stays dry. And if it is pouring down rain when you get to your campsite, your gear stays dry until you get your shelter set up. They should work equally well for anyone who might have to evacuate during flooding.