Most any filter will filter out sand/debris. Adding reverse osmosis after the sediment filter process would probably work best. If I weren't going to use the site for weeks at a time, I'd probably look to empty the tank before leaving and then not worry with left-over water. It would only take a few minutes to fill upon arrival
Since it is going to be "permanent" you could also look at more of a household filter set-up instead of small in-line filters. That would also allow for chlorine injection/filtering to make the water safer. While not 100% effective, it will get rid of most common nasties in the water.