There are lots of examples of printing from a button in the sample Accounting application that is available to download at http://www.suneido.com/support/downloads
I would suggest looking at the receivables invoices screen.
I don’t think the set option was designed to be used in a RecordControl. RecordControl will always set the controls values from what is in the record. If you want a checkbox field to default to true (checked), I would suggest using a rule:
The library record name would be something like: Rule_checkboxfieldnamehere, and the code will be:
function ()
{
return true
}