Fire works really well. Use a Harbor Freight propane weed torch wherever you see'em!
Or, if you are concerned with charring the interior of your 31F, ant bait, (as mentioned above), works too.
Years ago, in my PopUp, we came back from an afternoon of sightseeing to find our galley infested with the little critters. I had inadvertently setup on the campsite with the slide-out in direct contact with a bush, and that's how they got in.
I cleaned up all that we could find. And used bait traps to make sure. No more ants ever seen again. And I didn't even need to roast my camper.
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