Just a thought, but if you write "WWOOFer" and "WWOOFing" (note the capitalization) then it'll be clear (to those not yet in the know) that WWOOF is an acronym and that the words you're using are intentional and not errors. It's also good to expand an acronym on first use as a courtesy to the reader, as in: "I want to begin in Ireland with the WWOOF (World Wide Opportunities on Organic Farms, or Willing Workers on Organic Farms) association". Interestingly you actually wrote "wwofing" with a missing "o", and your correctors didn't correct it, so it's possible they weren't aware of what WWOOF means or stands for. I had to look it up, myself. :D