I recently just finished painting a pair of old benches that I picked up. I went through and spent A LOT of time sanding them down to get a good surface for the paint to stick to.

I used exterior acrylic paint and painted the sides of the benches with 3 coats and the tops with 4 coats (thin coats, I needed so many to cover up blemishes etc ).

My question is, is what I did enough? should I follow up with some kind of sealant? These will be covered during the winter, but during the summer months they will be exposed to the elements.
After all the time I spent on them I want them to last a few years before they need touching up.

Here's a picture of them (this is before).