I haven't done this yet, tents are still new enough, but I've read a few people here say to use a drill with a clothes hanger wire bent to form a sort of whisk shape. Makes sense to me, same idea as a blender vs using a mortar/pestle to make pesto... good luck ever getting the pesto smooth with mortar and pestle, easy with a power tool, I know, I tried that for a while (pesto by hand that is, same idea, oily thing mixing in with something you want to blend perfectly into the oil). Power whisk type thing is what I would do in this case, then add in a bit more mineral spirits and whisk again with drill if it starts setting.
This is one reason I decided not to use silnylon fabric on my recent backpack project, I was debating it, but opted for very nicely coated 70d, which, if you add in the extra weight of coating again silnylon, starts looking better and better all the time. Keep in mind there's a huge range of coating thickness and quality for pu coated nylon too.