I really don't wont dead mice in my trailer, that is why I won't use D-CON. Another problem is the trailer is in a storage yard and I am sure the owner of the yard would not want exposed poison laying about in his storage yard.
It used to be that the critter would have to ingest the poison first, which would make him thirsty and when he drank water it would activate it. Thereby causing them die somewhere not in your house, trailer, truck....
I don't know about now.
And if the property owner doesn't want poison laying about in his facility, then maybe he should do something about the vermin in his facility. To me, he has a fiduciary duty to protect his customers. (he won't and we both know it)
I hate poisons, too. Don't like the idea of local Hawks/Owls/Falcons dying from the posion. The neighbor's cats? I could live with that. Farm Cats? No. Outdoor cats are cool.
Short of sitting outside with a pellet gun all night, I don't know what else you could do. Setting a bunch of traps under the truck would make sense.
Maybe see if you can buy a bunch of Raptors: Owls, Falcons, Hawks.
And we're back to poison........
Maybe if you policed the area diligently every day while using it, it would cut down or even eliminate the friendly fire problem.
Good luck to the OP and anybody else with the problem