Yeah, I'd just go with conformal coating. Most are clear I think. Unless you use epoxy or find some that isn't. But yeah, why is clear a negative? I would think it was a positive?
As far as an actual solder mask, at least what's used on a PCB at the end, isn't something you can do by hand so they don't realy sell it like that.
And you should definately not use the TEchspray solder mask. THat is meant to be removed after a solder job is finsihed so it has been designed not to be permanent.