I remixed the Axolote Hex tiles to make wall-only connectors that make it easier to use the walls without the hex bases.
The posts come in 4 configurations of 90degree walls and 2 configurations of 60degree walls.
The + Corner is a four way junction.
The I connectors is a two way junction for a straight away. It also works as a spacer so you can intermix short and long wall segments if you need.
The L corner is a normal 90degree turn corner
The T corner is a three way junction.
For Gloomhaven it looks like most scenarios need about 12 each of the T and L. You may need a few of the + and as many of the I connectors as you need to supplement your walls. Not many.
The 60 and 120 corners looks like you need about 12 each to handle most maps.
This should make it so you can either on or off the hex bases link together walls directly and make nice perimeters.
I've only done the dungeon set.
If someone wants to expand this for the other sets clone this tinkercad drawing and remix away.
(released with permission from Daniel Ehrli via facebook)