Hi Wayne,
Soldering the end cap is fairly strait forward if you follow some basic soldering rules.
First you need to thoroughly clean and sandpaper the surfaces to be soldered.
It is very important to use a good soldering flux, and add it to the surfaces before mouting the end cap into place.
[ Guests cannot view attachments ]
The size of the burner is impotant too, but for a small boiler a dremel size burner will do the job.
You will need to be able to apply enough heat to keep the tin flowing.
[ Guests cannot view attachments ]
You need to pre heat the surfaces well before adding the soldering tin.
Once the end cap and the boiler reach the right temperature the tin will flow easily into the gap between the cap and the boiler, do not add too much tin at the same spot but let it flow away and keep on heating evenly.
Keep in mind not to overheat, keep it at the temperature where the tin starts flowing.
[ Guests cannot view attachments ]
After you have fully filled the gap with tin leave the boiler cool down slowly and cleanup the solder surface.
[ Guests cannot view attachments ]
I suggest you play around with some old brass or copper part, just to get the feeling.
good luck,
Maurice