I just completed the OTW Type VIIC U-boat hull with the Brass Tower. The tower wasn't impossible to build, but difficult to solder together at times. I used a small hand held butane torch and got the best results... There were times I tried to use a propane torch, but I had to limit it's use because the higher heat would warp the brass. Building a complete boat from Brass sounds like an interesting project... the best of luck!
"A man's got to know his limitations"
Harry Callahan SFPD