your gas struts must nearly lift the lid themselves. Lock it. Mine it takes a lot of pushing to raise it and I don't normally lock it, it stays closed at highway speeds.
I have been using TomTom for a couple of years and I would not leave home without it. But it has been droped from their range. I don't drive in the cities much but if I did I would look for a model that is cheap to update the maps.
I have had this problem since day #1, the dealer said that he fixed it but no. I took it back again and then his advice was to rev it a bit before moving. WALOC. So after 12 months it is still the same and I expect it will not change.