I made a custom transaction body field. A checkbox I default to 

checked

 and I made it hidden. Value is coming in as false on create. Anyone know where I might be going wrong?

sounds weird, does making the field display normally change anything

Is this in user event or client script? Are you checking the value before save or after? I think in the case of user event script, before submit on create the body field is going to not 'T' until after submit. A client script maybe different bit I still think it's going to Not 'T' until submit. If you expose the field and manually click it the client script will return 'T' I think.

This isn't in any script. Just within the Netsuite UI, I am defaulting the field