Yup, if you can't get to the back you are using a bandaid. The plate is the best idea. Those toggles are used for hanging pictures and fictures in drywall, not supporting a 150lb + person putting 500lbs of preasure on the seat after coming off a wave. Then you will really have a mess when these let go. You can rent a 6" hole saw for $10 and be done in 15min each side. Buy the cover and a few stainless screws and you are done for good. I like closure, I hate wondering. Thats why I am single now. Depending on the space between screws, the toggle hole will really compromise the integrity of the deck and when they pull loose you will have a giant hole that is unusable again. With the plate, use nylon lock nuts. I can't believe this was not done the first time. Screws will always strip and pull out. You would never screw a wheel to a hub now would you, you bolt them. Where do you live, I am on my way with the hole saw. One thing, be sure you are not hitting a stringer with the holesaw.