The presence of mouse traps does seem to be a clue. Mouse nests, turds, and urine seem likely.
Before getting too nosey in that area, read the Hantavirus info at the CDC -- here's the link:
Notice they mention fresh, as in "Individuals become infected with HPS after breathing fresh
aerosolized urine, droppings, saliva, or nesting materials."
Also, they say " Hantaviruses have been shown to be viable in the environment for 2 to 3 days
at normal room temperature."
So as long as you don't have any mice currently living in your trailer, you should be fine, at least as far as hantavirus is concerned.
The way I would attack this problem is to disconnect the trailer from AC power, disconnect any batteries that are in or on the trailer. In other words, disconnect all power sources to the trailer and all power sources that are in the trailer. Now if you accidently short-circuit some wires it won't have any effect.
Then I would clean out that whole area, moving the wires about as necessary to really mop, wash, and bleach everything in there. If you have a converter, battery
charger, or other electronic equipment in that area (not just wires), they may have to be removed and cleaned or replaced. Whatever you do, do not get water or any other liquid on or in any electronic equipment.
You will need to get access to the area behind the tank. Look it over and determine the best way of getting there.
Once everything is cleaned, let all the wires and connections dry out. Look carefully for gnawed insulation (rodents find certain kinds very tasty) and replace any wires that have been damaged.
Then you should be ready to reconnect the batteries and AC power.
I look forward to hearing how it all turns out!