Just to follow up on these darn things. The two large tarps have done great doing the sil treatment on one side (the outside). It took 1 full tube of silicone to do both 12x12 tarps, mixed 4:1 ratio with the 4 being the mineral spirits.
The last few days here have been great outside, so I took the opportunity to take care of our two smaller Guide Gear Tarps. Again only doing the outside. For both of those it took half a tube of silicone total. With our small ones, I did not go through my washing phase that I did with our large Guide Gear tarps and wasn't as worried since we don't use them as often. I just went with mixing my sil solution and putting it on. Regardless, it did soak in, so that's a very good sign. For those of you having to deal with this fiasco, I don't think you need to wash them first.