does anyone use Boomi to connect to Netsuite?

yes we do

Do you connect any ecomm platforms to netsuite for transactions? I am trying to write to a handling cost field and it will not write even though the internal ID and value is hardcoded in the map. Do you use handling costs in Netsuite?

we don't, I'm afraid. Does your custom form have the fields enabled for entry? If they're not, often integrations will fail silently