Repairing worn out rain gear seems like an exercise in futility to me. Repair one hole; wear it out in the rain to find 5 more. Hopefully it is only the seams that are leaking, but who knows? You would probably need to remove the old tape too which could further damage the garment and surrounding waterproofness. To me it is a task for someone who just can't emotionally give up on a garment.

If you are too busy to make the pants, I would buy the Frogg Toggs and see how they work out for your intended use. With rain gear the stuff just tends to wear out. I don't buy for the long term. I buy expecting to replace it in a few years.