DD,

I do the same as you with the spray on silcone (Camp Dry brand is what I use). The stuff works great and has always kept me dry. I also use seam sealer on all major seams for both the tent and the rain fly for the tent.

I think I applied that latter a little too thick on my Eureka Spitfire It dried but it still sticks to itself slightly, two years after I originally applied it.