Hello. So we purchased a new Shasta Oasis 25rs in January 2016. The tires are 205 75 14 load range c. Constancy tires. (no doubt made in China) We drove it to Seattle and back to Salt Lake City approx...
I replaced my factory Cs with Ds and I'm about a thousand pounds lighter than you are. You seem worried. Do it. I've had one tire blow on this TT and it isn't fun.