The root cause of chafing and fungal infections is moisture. Loose clothes with plenty of ventilation will prevent these problems most of the time. When it doesn’t, use only DRY lubrication during the workday. You can use medicated powders, but they’re expensive compared to simple cheap cornstarch which can be used in large quantities. All you have to do is pull your rig in the back corner of a commercial lot and step outside your truck to apply a whole heaping handful of it.
After work, you can get creative with medication. I used to get the “itch” and would soak a wash cloth with a Hydrogen Peroxide - Alcohol mixture and burn-scrub the nether regions for relief. But again I realized the problem was residual moisture from putting my pants on before I was FULLY dry. After a shower, I’ll use a blow-dryer to dry my hair (if you know what I mean). Since I’ve been doing that, along with wearing ventilated attire, the “itch” is gone and rarely have to apply the starch.