Re: Holy bottoms
TIN boat, right?
For the bilge drain, you can use blind closed end rivets. If the drain is the ONLY rivets you'll need to install, replace, etc, you can probably use a typical hand pop riveter. BUT the closed end blind rivets are much harder to 'pop' then normal rivets, some hand pop riveters aren't up to the task.
Because they're closed end, there is no thru hole. Dip the rivet in some 5200 before installation. The rivet head would be on the bottom, so once installed, you can fill the mandrel hole w/ 5200 too.
May need to shop for the closed end blind rivets online.
HarborFreight has a larger hand riveter for @$22:
Most of the tin resto's that require LOTS of rivet work, buy an air riveter, also @HarborFreight @$45:
If you & a really, really good friend are up for the challenge & the noise, bucking solid rivets would be even better. A substantial sledge hammer could be used as the bucking bar against the head of the solid rivet.
What motor & what hardwood are you planning to use? As Ondarvr mentioned, plywood would be a better choice. Many tin boats of this vintage had a nice piece of wood on the exterior of the transom, and you could replace it w/ similar. W/ a smallish 10hp +/- motor hanging off the transom, many have used similar as the interior structural transom wood too. Your boat is rated for an 8hp, so I too would consider sealing up a really nice piece of wood on either (both even) sides of the transom.
Pix of your Seaman would be great!