Eric,
Yes, that is how the sail panel to roof seams were done. Can't say I have heard of anyone leading patched panel seams but it certainly is possible. However, I am guessing the learning curve might be pretty steep, I have done a lot of soldering over the years (as a hands-on EE and have done a fair amount of plumbing too) and getting a panel joint well "tinned" and keeping the heat right (too hot and warpage will occur, too cold and the lead will not flow/adhere) could prove quite challenging in my estimation.
Having said that, I have no practical experience to lend.
Why do you feel that plastic is not a good way to go? Works for 99.9% of the people/work out there.
Good luck in any case and let us know what you decide/how you make out.
Regards,
Bob