I've been using Kiwi Performance Fabric Protector Camp Dry...
First Gear typically has "Hypertex" that is a thin breathable and waterproof membrane. The material is just the outer layer of sandwiched materials. My Firstgear HT 2.0 overpants have been used as riding gear and winter gear for two winters now. The outer cloth is just starting to look like it absorbs water but in a couple downpours riding to work this spring they don't leak past the Hypertex.
The Camp Dry just helps the outer material repel water droplets really well. I've used it on my 1994 Eddie Bauer Down Parka made out of original Gortex - after treatment have washed my hair in a forest downpour while wearing the jacket. Not afraid of getting the down wet, the water repellant works so well. 2011 I still grab that parka when the temps drop and freezing rain is in the forecast...
I started using the Fabric Protector Camp Dry because the Hypertex membrane is made out of some thin micro-perforated polyester or something. I was worried the solvent based old Camp Dry would harm the new membrane.
I use Camp Dry on my Joe Rocket endurance jacket as well (similar to a Kilimanjaro 4.0) Works great!
Whatever you do - Don't put your garments in the dryer after washing in cold water on gentle cycle! Hot heat of the dryer will melt the Hypertex membrane. High performance weather garments need to follow wash instructions such as gentle wash or soak and hang dry.
By the way congrats on the FirstGear stuff
Good stuff!