Is there a reason why you cannot use 5-gallon carboys or better bottles? My primary volume is about one gallon larger than your primary volume. I use 5-gallon better bottles and carboys along with 5-gallon and 6.5-gallon buckets (I use 3-gallon better bottles as secondary storage tanks when keg space is not available). A bucket is better if you want to crop from the top, but you have to use a true top-cropper to make the best of the technique. What strains do you use?