OK to sweat a threaded valve connection?

Hi, I'm in the process of installing a new Kohler rite-temp valve in my shower, and I'm having some trouble with leaks on the threaded connections to the hot and cold water supply pipes. I've tried a couple times so far using 2-3 wraps teflon tape as a thread sealant, and I've really tightened the connections down- but both times the connections have failed a leak test when I reapplied water pressure to the system.

I'm starting to get pretty fed up with this, and I started thinking- couldn't I just sweat these connections? I haven't ever seen someone solder a threaded connection before, but it seems like it would work. The installation manual doesn't specifically say anything about sweating the water intake connections, but it does say to disassemble the valve and remove certain parts to protect them from heat if I solder on the valve, so I'm guessing it's ok.. right? Any tips or suggestions would be greatly appreciated. What would you do in this situation? Sweat a threaded connection, or should I try something different first? Thanks!

Are these male threads on the valve body? If so, they are made to connect with either female adapters or 1/2" copper that will slip into them. If they are female threads then you can flux the female threads of the valve body and the male threads of your adapter and solder them after removing the plastic components of the faucet. If you dont really want to solder the connections try using 4-5 wraps of teflon tape and a coating of pipe dope.

The Kohler valve has two options.

With that valve, you can either use the FA fittings and thread over the ends.
or you can insert a pipe inside the ends and solder it.
If you use pipe, remember to flux it.

it worked

Thanks Terry and RioHyde for your suggestions! It didn't even occur to me that pipe could be inserted into the ends there. Before I tried soldering it I decided to give it one more shot and tried RioHyde's suggestion of 4-5 wraps of tape and pipe dope. Bingo- no leaks! Phew, it's a relief to have this project finally finished. Thanks again, and thanks for the great forum Terry.