The blank page is probably a php parsing error. You can look in the directory that holds the form and see if there is a page named something like error_log. You can change it to error_log.txt to make it viewable within a html editor or word processor. It will point to the line in your page that has the error.
As far as the inputs go I posted how yours would look assuming your using the same form for testing.
<input name="TrailerA" disabled id="item80_text_1" type="text" maxlength="254"
data-hint="" autocomplete="off" value="<?php echo (!empty(array_sum($sumTrailerA)) ? array_sum($sumTrailerA) : '');?>" />
All you actually need to do is add this to each trailer input.
value="<?php echo (!empty(array_sum($sumTrailerA)) ? array_sum($sumTrailerA) : '');?>"
This one is for Trailer A so add it to the other inputs and adjust the variable names to meet that Trailer name and the Cumulative input.
All were doing is adding the value="" attribute to the inputs and having php fill it in.
Take your time. We'll get you up and running.