When I store our trailer in the winter, we mothball it using about 2 boxes of the round mothballs and envelopes. We buy the a box of 3 1/2 x 6 1/2 envelopes and use a hole punch to place several holes in the envelopes. We then place several mothballs per envelope and seal the envelope. I then place all of the envelopes througout the entire trailer. It is easy to toss them anywhere in the trailer. What is nice about this is there isn't any mess to clean up once they are in the envelopes. Also, you can re-use them for a couple of seasons. When we remove the envelopes, I place them in a zip lock bag and keep them in our garage until I use them again in the fall to store the trailer. We've been doing this for over 15 years and have never had any mice in the trailer during storage. The only thing is in the spring, it may take a couple of days to air out the trailer.
2011 Jayco Eagle Super Lite 314BDS
2013 Chevy Silverado 2500HD CC 4X4, 6.0 Vortec, 4.10 axle
Reese Dual Cam Sway
Wife, 2 kids and dog