Other than the trouble every trailer has with loosening of the lug nuts, the weight of a fish won't even dent the capacity of the 8 inchers, which should be around 700-900 pounds each depending on the pressure.
You will have to stop several times during that 200 miles to retorque the lugnuts on the trailer till they stop moving around and take a set.
For some reason trailer tires/wheels loosen up more readily than the Tow vehicles.
I've never had trouble with lug nuts loosening on a trailer. Although I do check them on long trips. The reason people talk about not wanting to trail with 8" tires as opposed to 12" tires is because the bearings get more wear and tear on them. The reason: an 8" tire spins more revolutions than a 12" tire for the same distance. More revolutions means more heat and more wear. That said, as long as you take care of your bearings, keeping them greased and making sure they don't get water logged, you shouldn't have a problem. Most people don't do it, but my trailer mechanic recommends that you have your bearings checked and regreased or replaced and greased at least once a year. Especially, if you dip your trailer to put your boat in the water.
I recently took a trailer from Erie to Pensacola and back with 2 sunfish clamshelled on 8" tires. No problem. The total trip was almost 2200 miles. The tires did have less tread at the end of the trip though. I averaged 70 mph, and frequently went pretty fast, especially in Alabama and Tennesee .
Re-pack your bearings before a long trip. Check your tires frequently and feel the center of the hub for heat. They should not be hot to the touch. If they are hot, you are going to fry the bearings which can lead to axle failure so if they get hot go much slower until you can get somewhere to get the problem resolved.
But really, a sunfish is so light that the biggest problem you will have is not enough weight to keep the trailer from bouncing all over the place. Most trailers are "over sprung" for sunfish needs.
.....Most people don't do it, but my trailer mechanic recommends that you have your bearings checked and regreased or replaced and greased at least once a year. Especially, if you dip your trailer to put your boat in the water.
Very good point... and I'd like to add this.... Install "Bearing Buddies" or a BB clone.
Dipping warm bearings into cool water pulls water past the seals as the air inside the hub contracts. Once grease mixes with water into a petrolium mayonase it no longer lubricates and you are done for.
...and you may never notice a problem on short trips. Catastrophic breakdown usually happens when you run at higher speeds for longer distances.
I think bearings still need to be checked yearly, but after adding "buddies" to my hubs I haven't had to replace $30 worth of bearings each time, just $3 worth of grease.
If you don't choose to use BB's it's a very good practice to regrease and inspect bearings at the END of the season rather than preparation for a new season.