Thanks for all the people who have posted suggestions and genuine concerns about my mouse dilemna.  A bit of an update.

Saturday I hauled the trailer 1,800 km (1,100 miles) to a RV refurbishing place - the only one I could find that would take it on.  They pulled the roof off yesterday and found an unbelievable mess of dead mice, nests, grain, and a very disgusting mess of insulation and wiring.  They are pulling the insulation, sanitizing the roof and air conditioning, inspecting wiring and then will re-insulate, determine the access point and possibly have to tear into the wall in question.  They will then have to replace and seal the roof.

Pretty disappointing for a 2 year old trailer that is supposed to be so well constructed and supposedly had a good warranty.  Sundowner has labeled this "an act of nature / god" (after they told me I shouldn't park it near a barn).  I guess the courts will decide if it an act of nature / god or a predictable outcome for defective construction practices. 

I'm curious.  Is the RV place  you are having the extermination held . . doing it for free?  This was an interesting topic and I did a little googling and found that one of the top five reasons for RV insurance claims was . . . you guessed it . . . pest infestation, particularly mice. 

With a little research I found that it's nearly impossible to find a mouse proof environment, particularly horse trailers on farms.  Here's a picture of a sealed computer that was having trouble with  . . . guess what?  Those ARE mouse droppings.

 Any openings in your trailer or LQ that are wider than 6mm (a quarter of an inch or less than a width of common pencil) and you're in trouble: through a combination of squeezing and nibbling, the mice could well be moving in. 

 Here's more help:  http://www.icanrv.com/id42.htm

Unless cash is growing on trees around your place, I wouldn't spend a penny on lawyer fees. In your statement above you make two very important points. You park your trailer next to your barn, and the ceiling had grain in it. All the Sundowner boys have to do to win this case is prove that the grain from your barn, not their factory. You lose, they and the lawyer wins. That all being said their are lawyers across the country that will take your case all the way to the Supreme Court as long as you keep paying. I can refer to you to a couple that I rope with,.......... they need the cash for entry fees.

Talk a bout some top shelf individuals,........ team roping lawyers.

I need the answer to that one.  Someone owes me a new Xbox power cord!!!

Mice have been found in car/trucks too.  I guess we should sue all the auto manufactures as well.