If you need to gel windows in a way that will stay up for a long time, here's a popular and successful technique. I've heard a lot of DPs and grips pooh-pooh using squeegees to gel windows, but perhaps they don't know everything. I've done this dozens of times quite successfully. It does take a certain amount of practice and a steady hand, but it's also not rocket surgery. If it's your first time doing it, order a little extra gel to give yourself room to make mistakes.
