I'd suggest that a heavy wool traditional kilt is the best thing for heavy rain--virtually waterproof, and much better than wet trousers -- climbing breeches. Whilst as for waterproof trousers--much too hot and sweaty.

Too kilt adds a layer twixt self and ground when in bivvy-very welcome.

Whilst kilt itself comes to no harm.

Too having tried both on packing trips--much better putting on kilt in the morning than wet trousers.

James