but remember no stain/protectant is for ever, regardless of marketing or price.
I recommend and use commercially the following: CWF-UV by the Flood Company, comes in many colors and has to be hand brushed on. Second any stain protectant from the Wolman Company.
Stains/protectants that you spray on with a deck sprayer in general are to thin and only topical. There fore, In my experience the ones that you brush on are more thick and do soak in.
Remember, on both products, the first coat is really soaked in. YOu should apply two generous coats on the first application. Then after that you have built up a good base.
The main rule and it seems that you have headed it. Make sure the wood has dried out. Its like a wet sponge filled to capacity, you cannot add any more water until some has leaked out. A wet deck, green deck will not absorb as much stain as a dry deck.