How many miles did it take to wear down the tires like that? There are several possibilities. The inner edge is "scuffing" on the pavement, so I would check a couple of things.
First, alignment. When the axle was set, did you measure from the tongue to the center of the axle on both sides? The axle needs to perfectly straight with respect to the tongue, both wheels need to be the same distance from the front point of the tongue to the center line of the axle.
Second, Alignment. Park on a perfectly flat surface (concrete apron which looks very flat). Use a framing square to see if the wheels (tires) are perpendicular to the pavement. They should be straight up and down (no gaps at the top compared to the bottom), when the trailer is in the towed position behind the car and loaded like it is for a regular trip.
Third, tire pressure. Check the load rating of the tire. It will say something like 800# at 60 PSI (just an example, read the sidewall!). Figure out your rolling weight and see how it matches up with the combined total of the tire capacity. If the capacity of the tires is 1600# at 60 PSI and you are rolling with 900#, try dropping the pressure a bit (a little, not a lot). Normally, over-inflated tires will wear in the center. Under-inflated tires will wear on the outside edges.
Please let us know what you find about the tire wear, I'm sure others would like to know the results.
Hopefully, someone else with more experience will add to this post and provide better information and perhaps a solution. You could also do a bit of research on the web to see what's out there about uneven tire wear on trailers.
Here's a couple of links
http://blog.easternmarine.com/whats-cau ... read-wear/http://www.etrailer.com/question-40826.htmlGlad it was a good trip! Deet is our friend for those pesky critters. You might try spraying some deet in the cracks from outside where they're getting in until you have a solution.