The old jalousie windows are hard to beat. They tend to be very well built. Also very difficult to find a satisfactory replacement.
If they don't close completely, probably need to replace the torque operators. About $10 for a torque operator. Search online for a replacement that is same dimensions as original. They come in left and right versions.
You can either fix your windows, will take some time but not much money. Or you can spend a lot of money on new windows, that won't fit your openings. So then you will spend a lot of time modifying the window openings on your trailer. Its an obvious choice IMHO.