how to get rid of the smell

There are commercial grade odor eliminators. I successfully used one on a cabin that was infested with mice and pack rats. Several had died and decomposed in the walls, there was feces and urine, and water damage with rot and mildew due to broken windows. It took more than one application but the odors went away and have not come back. Here is one. SCOE 10X link

Plus they will buy it back, including shipping, if it does not work.

Thanks all! I think I will look into the rot doctor. Hopefully that will help with the smell and also protect in case we ever have a leak. I've fixed enough rotted framing already and do not want to fix more in the future.

Could the smell be coming out of the floor?

rjxj wrote:
If you have it all the way down to the framing I'd consider something like Rot Doctor 2 part penetrating epoxy. It will seal all the lumber for future protection and possibly help with any odors.

I think that might be a prudent idea. I did not even know what penetrating epoxy was until researching an exterior roof repair. I happen to use Restor-It which is basically the same type of stuff! Worked really well!

any places where a dead mouse might be??

If you have it all the way down to the framing I'd consider something like Rot Doctor 2 part penetrating epoxy. It will seal all the lumber for future protection and possibly help with any odors.

I routinely use ozone for odor remediation. It is very popular for flood and fire restoration. In a trailer I suspect a small 1-3 gr/hr generator would be sufficient to develop a shock level for a few UNOCCUPIED hours, then ventilated prior to occupancy.
I use a much larger capacity unit in my house occasionally with the same occupancy precautions. Although these devices must be used with caution, the ozone rapidly dissipates into oxygen. There is an allowable exposure limit, but the limit is so low (and barely over the human nose detection threshold) that if I can smell it I don't breath it.

Musty smell is usually a water leak. Any signs of leaks in the roof?

kilz worked for me when I had 5 male cats that had a turf battle. took a lot more than 2 coats however.
bumpy

Another recommendation for Kilz. Hides stains, ordors, etc. You can even get it with an embedded smell to freshen things up. Febreeze anything you are not going to paint. Air it out as much as you can.