Multiple choice items with custom format

Using html file, I set multiple choice items with Item type of "Custom".
e.g.,
<input type="checkbox" name="<ml.varname>_03" value="1">
<input type="checkbox" name="<ml.varname>_03" value="2">
<input type="checkbox" name="<ml.varname>_03" value="3">

The problem is that only the last selection of checkbox is recorded.
For example, if 1 and 3 are chosen, only 3 is recorded.

How can I make all checked items recorded?

It seems as though this problem may be able to be remedied by implementing three variables to intercept the data, and then changing the HTML as followed:
<input type="checkbox" name="<ml.varname>_0[B]1[/B]" value="1">
<input type="checkbox" name="<ml.varname>_0[B]2[/B]" value="2">
<input type="checkbox" name="<ml.varname>_03" value="3">

Does this make sense?