Scheduled SuiteScript to load a CSV from File Cabinet and append saved search results to CSV and save

I am attempting to create a historical csv backup (appended rather than overwritten) to our file cabinet using a saved searches results (on a once a week schedule).

I know its possible to write a saved searches results to a CSV (using task), but I’m not sure how I can append instead (maybe using file.appendline?). Here is what I’ve come up with which results in the appended data being “task.SearchTask” instead of the saved search results:

/**
 * @NApiVersion 2.1
 * @NScriptType ScheduledScript
 */
define(['N/file', 'N/task'],
    /**
 * @param{file} file
 * @param{task} task
 */
    (file, task) => {

        /**
         * Defines the Scheduled script trigger point.
         * @param {Object} scriptContext
         * @param {string} scriptContext.type - Script execution context. Use values from the scriptContext.InvocationType enum.
         * @since 2015.2
         */

        //[file ID, Saved Search ID]
        const keys = [
            [72567, 1701]
        ]

        const execute = (scriptContext) => {
            for(var i = 0; i < keys.length; i++) {
                var searchTask = task.create({
                    taskType: task.TaskType.SEARCH,
                    savedsearchId: keys[i][1]
                });

                var csvFile = file.load({
                    id: keys[i][0]
                });

                //This probably doesn't work...
                csvFile.appendLine({
                    value: searchTask
                });

                csvFile.save();
            }
        }

        return {execute}

    });

Any assistance would be appreciated!