No trailer tires are made to carry more weight and are designed to run higher pressures I have looked into this and trailer service is the best way to go. I found a place selling 14.5 trailer service 12 plys on the wheels at unbeliveable prices. http://www.easternmarine.com/14-15-and-16-Trailer-Tire-Rim/
Run what ever you like but I would definatly make them trailer service only for safety sake.
I put several thousand miles on a tandem trailer with regular old tires.....That's what was on it, so I used them. I did have a blow out once, but it was on a tire that was too low, and I decided to just run it anyways. I was dumb.
With that said, If starting from scratch I'd buy trailer tires. Changing tires sucks, and mine blew out on the way to Pittsburg, in the middle of the night, delivering a car I sold.....I thought for sure the tire ripped the side off of it. (thank god it didn't)
I am currenlt rebuilding my tandem trailer, new wood, new lights repaint...and tires. I called for new tires and they wanted over 400 for 4 new tires. I got on CR and found 5 Goodyear wranglers on new rimes off of a 2010 Jeep. THese tires/rims have less that 5 miles on them. 300 bucks I bougtht them and they look great on the trailer. No dought trailer special tires are tuffer and will most likely last longer however for my needs this will do me fine. Just my 2 cents.
IMO, as long as the total load rating is high enough with the 4 tires combined, I think you'll be fine. Figure if each tire can take say 2300 lbs x 4=9200 lbs take 25% away for saftey, that still leaves you at 6900 lbs...so on a 7k rated trailer, I think you'll be just fine...