How did the hole get there? If it is a pinhole, put a washer on a sheet metal screw and as mentioned, use JBweld or marine
and just screw it into the hole. You can also do the same thing with a crack, epoxy
a series of screws into the crack then cover them all with a coat of the stuff.
The main concern is if the pan is leaking because of internal corrosion
, as painful as it may be the best option may be to figure out how to replace it if you are planning on spending time somewhere other than a marina all the time. If it was caused by a dent of some sort of blow I wouldn't be that concerned. If you can at least drop the pan to inspect the inside, either visually or by feel often you can get an idea of the condition.
Needless to say, to have a reliable epoxy bond the pan needs to be drained and then degreased pretty good first.