js HTML Checkbox

I am not able to pull through a set of text if the checkbox is checked. JS and HTML below... Prob a simple fix - but I am lost that this is not functioning.

//js

function getTrainerExp()

{
    var trainerexp="None";
    //Get a reference to the form id="courseform"
    var theForm = document.forms["courseform"];
    //Get a reference to the checkbox id="includeexp"
    var includeexp = theForm.elements["includeexp"];

    //If they checked the box set trainerexp to ACMEEXP
    if(includeExp.checked==true)
    {
        trainerexp="ACMEXP";
    }
    //return the trainer expenses
    return trainerexp;
}


function calculateExp()
{
     var expense = getTrainerExp () ;

    //display the result
    var divobj = document.getElementById('trainerexp').checked;

    divobj.style.display='block';
    divobj.innerHTML = "Please Include   " +expense;

}

HTML

 <p>
<label for='includeexp' class="inlinelabel">If course delivery is at customer site include trainer travel costs and expenses</label>

<input type="checkbox" id="includeexp" name='includeexp' onclick="calculateExp()" />
</p>

<div id="trainerexp"></div>