HTML editor and custom fields

If I have HTML data in custom fields, i.e. .TABLE_HEADER, TABLE1, TABLE2, TABLE3 and insert it as shown (in order to put a customer specific HTML table in an email).  Breaking it up because the field character limit is 255.

[[custom.table_header]][[custom.table1]][[custom.table2]][[custom.table3]]

It is dropping characters and corrupting the HTML  These fields are 250 characters long (just in case).If I concatenate these fields from the contact list they render correctly - so the HTML is good.

Obviously I'm missing something - but I have no good way to see the HTML output of the resultant e-mail (since the e-mail reader messes with it so much).  (or is there a good way?)