: I am at the point to where I need to think about installing a seat
: in my 'Night Heron'. No idea where or what to use. I realize a
: type of foam or styrofoam might be good but what thickness to
: start with? Where to get it? etc...

What you need is mincell foam. It's somewhat flexible and just spongy enough, but fairly ridgid and holds whatever shape you grind into it. It also is a closed cell foam and it does not soak up water.

Here's a link to what you need for starters:

http://www.nrsweb.com/shop/product.asp?pfid=2076&utm_campaign=shop_comp&utm_source=google&utm_medium=buy_now&utm_term=goog_product_2076&gclid=CIn-sJnwlLECFdOa7QodTC-7hQ

Take it, trim it to fit your kayak, and then trace your buttcheeks out on it. (Please don't post pics of that). Then take an angle grinder and grind out a hollow to fit your butt. Word to the wise, and this is going to sound silly but I'm serious here- don't leave a ridge in the buttcrack area. The first seat I did I made it fit my butt perfectly with a nice recess for each cheek and it was not comfortable at all. Don't leave the ridge up the middle. It's like having a wedgie all day.

There's really no way to describe making a seat without getting into the gory details! Once you get it rough shaped the way you want, use sandpaper to smooth it out. The link above has glue that you can use to glue it in. You can make a backrest the same way, or knee braces, or any other padded item.