No ian - in my eyes to spend thousands on a holiday , claim its for charity and get cheap kit to do it while raiseing a small amount is wrong. You are spending hundreds for every £ the charity gets
You intended to use charity money to pay the whole thing originally.
anyway I have said my piece and more. I do hope you have a great time and if you do go on to volunteer to build a school then that is great and moethan many will do. I just wish you would be honest about your holiday
I have done a few similar things myself - and did not rely on any charity to pay for it.