RE: Scratch Designed/Built Sailplane
The plastic covering films work fine on slower flying models even up to 3 meter span gliders. For a faster powered or contest sailplane where high speeds will be regularly used then I like the security of proper hinge with some sort of sealing film or tape. In the case of a sport glider such as what Nodd is doing here I'd be using the film hinges as well. Simple, clean, and workable for a model such as this.
Nodd, the first sign of any possible "hinge distress" will tend to show up on the longer hinge lines such as on the ailerons. This can occur if the wings flex up under load and you're flexing the ailerons at the same time. So keep an eye on all the hinges but especially the ailerons.