On my other trailers i used some small fiber mesh and glued it on the inside of the openings to keep out the bugs, but you better check with the dealer because i also just bought a sunset trail SR32RL and durning the walk around they told me if i was to do that the warranty would be no good and will not cover anything that went wrong with the frig. or hot water tank, you could always cover the vents when parked and not in use and take them off when you going out for a trip i guess that's what I'll be doing now.
It is not the model of TT you have but the appliances installed it that dictate the screens you need. You should have got a manual for everything installed in your TT.
I know exactly what your going through as I just did the same not long ago. I just went out and measured my areas. Then ordered the screens from Amazon. They all fit perfectly. During our walk around, Camping World recommended that we install the screens. I assume they just wanted to sell screens.