If you are looking to put a great protective cot on the bottom, use Steel Flex epoxy. It's a two part epoxy, and it may even come in clear, just need to call them and ask every question you can to a man named Jerry, he is very helpful. In fact, this stuff was created for Jon Boats, particularly riveted hulls. I used it twice - once each for my boats off craigslist - and it looks great. The bottom half of my boat is done with the Steel Flex, and the top blue portion is Interlux Brightside, Sapphire Blue. I have attached a picture to show you what I mean. A lot of guys over at tinboats.net and I have used this stuff - they have used a lot of colors, one of them olive drab green for duck boats. Below is the website. Do some research, but this stuff is bullet proof.
http://fascoepoxies.com/
Here is a link to my boat modification I started not so long ago:
http://tinboats.net/forum/viewtopic.php?f=13&t=8277
PM me with any questions.