Well, once I actually climbed under the trailer, I discovered the hole was only 1 1/2" diameter, but there was another 1/2" hole in the bottom, and a crack running between them.
I no longer have access to the hot air plastic welder I used in the past, so I purchased a
soldering iron type & some polypropylene filler rod.
The repair wasn't pretty, but there is now a double layer of plastic covering the holes & filling the crack. I then added a layer of epoxy to add some strength to the repair, (no photo) and finally, a layer EternaBond Tape over the entire thing.
Filled the tank, let it sit a couple of days & it held. Hopefully, a permanent fix.