I found a way to add user input field on any shipping option. I thought I would post it for other who may need this.

1. add custom field to shipping options page: follow these instructions https://www.zen-cart.com/showthread....ld-to-Checkout
Doing this would be enough if your add the field to the end of /includes/templates/template_name/templates/tpl_checkout_shipping_default.php shipping options if you only have one shipping option or the field corresponds to the last shipping option.
2. If you want to add the field to 'NOT the last option' and you have multiple options, then:
EDIT /includes/templates/template_name/templates/tpl_checkout_shipping_default.php
FIND
PHP Code:
<?php echo $quotes[$i]['module']; ?> <?php if (isset($quotes[$i]['icon']) && zen_not_null($quotes[$i]['icon'])) { echo $quotes[$i]['icon']; } ?>
<div class="important forward"><?php echo $currencies->format(zen_add_tax($quotes[$i]['methods'][$j]['cost'], (isset($quotes[$i]['tax']) ? $quotes[$i]['tax'] : 0))); ?></div>
<?php } } else {?>
<?php }?>
<?php echo zen_draw_radio_field('shipping', $quotes[$i]['id'] . '_' . $quotes[$i]['methods'][$j]['id'], $checked, 'id="ship-'.$quotes[$i]['id'] . '-' . str_replace(' ', '-', $quotes[$i]['methods'][$j]['id']) .'"'); ?><label for="ship-<?php echo $quotes[$i]['id'] . '-' . str_replace(' ', '-', $quotes[$i]['methods'][$j]['id']); ?>" class="checkboxLabel" ><?php echo $quotes[$i]['methods'][$j]['title']; ?></label><!--</div>--><br class="clearBoth" /><?php $radio_buttons++; } }?>
CHANGE TO
PHP Code:
<?php echo $quotes[$i]['module']; ?> <?php if (isset($quotes[$i]['icon']) && zen_not_null($quotes[$i]['icon'])) { echo $quotes[$i]['icon']; } ?>
<?php // ** start modifications by hayden thring www.hthring.com ** // if ( ($n > 1) || ($n2 > 1) || ( $quotes[$i]['module'] == MODULE_SHIPPING_STOREPICKUP_TEXT_TITLE) ) { if( $quotes[$i]['module'] == MODULE_SHIPPING_STOREPICKUP_TEXT_TITLE){ ?>
(Carrier Name: <?php echo zen_draw_input_field('frequent_code'); ?>)
<?php }else{ ?>
<div class="important forward"><?php echo $currencies->format(zen_add_tax($quotes[$i]['methods'][$j]['cost'], (isset($quotes[$i]['tax']) ? $quotes[$i]['tax'] : 0))); ?></div>
<?php }// ** end modifications by hayden thring www.hthring.com ** // } else {?>
<?php }?>
<?php echo zen_draw_radio_field('shipping', $quotes[$i]['id'] . '_' . $quotes[$i]['methods'][$j]['id'], $checked, 'id="ship-'.$quotes[$i]['id'] . '-' . str_replace(' ', '-', $quotes[$i]['methods'][$j]['id']) .'"'); ?><label for="ship-<?php echo $quotes[$i]['id'] . '-' . str_replace(' ', '-', $quotes[$i]['methods'][$j]['id']); ?>" class="checkboxLabel" ><?php echo $quotes[$i]['methods'][$j]['title']; ?></label><!--</div>--><br class="clearBoth" /><?php $radio_buttons++; } }?>
change MODULE_SHIPPING_STOREPICKUP_TEXT_TITLE to the title as defined by the shipping option you would like to add the field on.
You can find the above code (way to add additional area on at end of any shipping option) on https://www.zen-cart.com/downloads.php?do=file&id=1224 (\Shipping_By_Quote_2.3.zip\Shipping_By_Quote_2.3\includes\templates\spyworld\te mplates\tpl_checkout_shipping_default.php)
This would not be the best option if anyone has already created a plugin that add field directly to the shipping_way database field, but I don't think anyone has.