How my outdoor connection really should have been done?

Outdoor forklift battery is a tall and skinny 24 volt 1652 pounds hooked up to electronics inside a watertight shed. The battery is not going to be moved unless you volunteer. Auxiliary system that I used to power a large chest freezer for ~ a year. Then the clamp connections eventually went bad right after topping off the battery cells.

Battery is almost up against ceramic coated cinder block that does not lend itself to drilling and attaching stuff. So I used 1/4" bolts to connect the charge controller lugs to the very large battery lugs. It is a forklift battery, the lugs that connect the built in 2/0 to the inverter are quite large.

The bolted connections also worked for about a year in this desert environment. Corrosion eventually ruined the connections and attempts to revitalize the connections also failed.

Decided to "hard wire" the dang thing. Drilled out the bolt holes to remove corrosion. Removed corroded ends of charging 6AWG wires, only the positive wire showed substantial corrosion. Jammed the wire ends into the drilled bolt holes and used solder to create a "weathertight" connection. The solder created a solid connection but it is far from weathertight. Planning to cover the connection with Master Seal High Performance Polyurethane Sealant.

This should work. Shoot, the previous connections were 10 times "sketchier". But I have a feeling there was, or is, a better way to do it.