I do actually believe that the Long barrow form can be symbolic of upturned shallow boats

As stated recently on prehistoric-britain http://prehistoric-britain.co.uk/ten-thousand-year-old-boats-found-on-northern-europes-hillsides

I do think its possible that these long barrow form boats, are symbolic to the layout formation in line with the hill forts along the river route from the pennine's.. & is  symbolic of the ancient shallow boat-like punt craft that were used for travel. especially if travel to places like the Nottingham caves was possible and the Scottish coastline, Ireland, Wales & beyond as regular inter connected waterways

Irish schoolboy discovers 4,000-year-old boat in Roscommon (irishcentral.com) https://www.irishcentral.com/roots/history/irish-schoolboy-discovers-4000-year-old-boat

Image of ancient boat

https://ibb.co/NtWbFLb