If the tank gets dirty then so will the probes.
So while it may seem like a good idea, it may need to be cleaned periodically for best results.
Somewhere I read about a level sensor that used some sort of circuit to self clean the probes using electrolysis some how.
Back to thread base: enclosure building/cutting/specifying is a matter of Practice.
My techniques/toolings/sources will differ from most anyone else here, as will theirs' from any others.
Classic "time in the saddle" stuff. I have techniques that scare hell out of others (freehanding an endmill??)
BUT, it works for me. Just as you have to develop what works for you. Good Hunting <<<)))