I'm witnessing some diesel leaking at the fuel supply connection into the tank on the drivers side. I laid a plastic cover on the ground to get an idea of he amount. It's about the dia of a soup can lid in a 24 hour period. The tank is about 7/8 full. I can't tell exactly if the metal tube attached to the tank is threaded in or flanged in .... laying on my back I can't quite reach up to clean off the little bit of soil that has been collecting. Question is ... is there a sealing epoxy that can be applied externally to stop the leak? The coach is an 06 Beaver Monterey.

Make sure to check your rubber hose  as mine was rubbing on the frme an had a small pin hole in it. I got another piece of hose an slice an clamped it on. Also tied the hose up so it wouldn't rub. That also helped when filling the tank pump not shutting off as much. This is on an 06 Montery.

I experience a similar small leak in 2008 Contessa, and after further looking found it to be coming through the cap, leaking onto the inside of the door and dripping down overnight.  The end of the filler tube is very rough and the seal on the cap didn't seal.  Just another place to look.
Mike

Check your hose clamps as cold weather can cause hoses to contract allowing a small leak. Happened to me this year with the heater hose and a turn and a half on the hose clamp cured the leak.

A two part epoxy like Liquid Steel will seal a porous weld if it is applied properly in a non pressurized tank. The most important factor in application is cleanliness. If there is any fuel or dirt on the surface of the metal it will no work, so if the tank is full and still leaking it gets to be very difficult to clean.

If the leak is in a threaded fitting, it is best to remove the fitting and apply a Teflon thread sealant and reinstall to correct the leak. If you try to correct a leak in a threaded fitting with epoxy, it is very difficult because of the need to clean the fitting all of the way around it and apply the epoxy all of the way around, and it is very difficult to adequately clean the threads.  

That being said, look very carefully at the fuel filler hose as at least 95% of fuel tank leaks are these hoses.

Gerald