Have you checked the tread and/or age of the tires on your trailer lately? Tire Rack has the new tires that you need for your trailer in 13"-16" load range C-E — the Goodyear Marathon Radial, specifically designed for trailer use. The Marathon Radial is Goodyear's special purpose trailer tire designed specifically for use on travel trailers, pop-up campers, boat trailers and fifth wheel trailers.
Get more information, pricing and availability.

We do carry the Goodyear Marathon Radial Trailer tire in 205/75R15. To check prices, click on the link in the blog.
The only two trailer tires we carry are the Goodyear Marathon Radial, and the Power King Towmax. Both tires are available in 235/80R16. Click on the link in the blog above for pricing and availability.
In ST235/85R16, the only brand we carry is the Power King Towmax tires, currently selling for $141 per tire.
We carry two Radial trailer tires in this size, the Goodyear Marathon Radial Load Range C and the Power King Towmax STR load range C or load range D.
I'm sorry, Tire Rack does not sell any tires in those sizes.
I'm sorry, I'm not sure where you can find 17.5" trailer wheels.
What is the bolt pattern, diameter and width of wheel that you would need? If you can provide that information, I can check to see if we have one that will work for you.