To get around the problem of sand dropping off your bases, give them a coat of heavily thinned pva (thin enough for the sand to soak up) before you get to the priming. So, PVA and sand/gravel. Wait to dry, then thinned out PVA mixed. Once fully dry, prime.
I've been toying with the idea to actually finish the bases completely (including static grass) after I've put down the first base coat layer of colours. That way I might be able to stop painting certain miniatures earlier and settle for a "good enough" standard on rank and file.