Epoxy will work fine.
Seconded, I used standard JB weld on pin holes, it's held for 3 years. Make sure it cures fully or it will peel off like a scab when the gas finally eats through.
That can mean letting the tank sit without fuel for 48 hours in a warm place, ideally letting it sit for a week in the house will ensure it is fully cured.
Rinse the tank with acetone after draining and leave it open and use a hair dryer or heat gun to get the tank to dry out.
If you have pinholes there you probably should do a good look with a boroscope or mirror and light to check the sides and corners of the tank as well as the top.
If they sanded through it sounds like your tank has some rust problems that would probably be best dealt with to ensure long life. Caswell's and POR-15 tank kits are some of the best available and Caswells had been on sale a while back. Check prices for either at various bike suppliers and amazon, etc for best price.
David