Building my own plastic conical

Hello,

I just purchased two 15 gallon US Plastics induction tanks and intend to make a pair of conical fermenters out of them.  I’ve found some great ideas on line for sealing the lid and building the dump valve at the bottom.  I am looking for some advice as to how far from the bottom of the tank do I drill for a racking arm and how far should I drill for a thermowell?  If anybody out there has built their own I would love to hear any advice you may have.  Thanks!