I haven't had root rot problems but I have had some Erwinia problems with these.
They don't like high temps, but they like a fair amount of light. Besseae like conditions. The highlands of New Guinea can get pretty cool. When I was working at the zoo we got some Bolin's pythons from PNG highlands, and the capture info included how everyone needed jackets to stay warm.
Anyway they do better in my phrag area than in the multi paph area of my GH. Typical CHC Antec like mix with a good portion of oyster shell added.
great to see a good example of this species. There are quite of few 'impostors' floating around where it is not clear they are the 'true' wilhelminiae, your plant looks like the real deal, a true to type wilhelminiae. Glad it is growing well for you. Some of the impostors are (adductum x praestans) often sold as gardneri. Some impostors are really praestans.