@ Thanks!
I worked on your suggestions for a bit without success and then found this: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums, which allowed me to add and use:
#include "LowEntryExtendedStandardLibrary.h"
Unfortunately, this line:
TArray ULowEntryByteDataEntry PacketByteData;
(post does not like the left and right angle brackets around the type, so these are omitted here but not in VS)
generates an error:
Error C2139 'ULowEntryByteDataEntry': an undefined class is not allowed as an argument to compiler intrinsic type trait '__is_trivially_destructible' Colony2 e:\epic games\ue_4.21\engine\source\runtime\core\public\Templates\IsTriviallyDestructible.h 18
So I still have something to sort out. 