When we leave the property these are the things we do.
1) Leave all doors open to allow air circulation, this includes any under stairs cupboards and wardrobes.
2) Leave some sort of freshner inside clothing drawers even if it's a bar of soap.
3) Squirt the long term cockroach spray across the doorway on the floor. This means any insects that cross the threshold will die and not breed.
4) Cling film all sinks and toilets, this prevents anything crawling up them and stops bad smells. If the water in your "S" bend in the sink or the level in toilet goes down due to evaporation you can get problems.
If anyone has any other tips would be interested to hear.